DS2502+T&R - Maxim - Datasheet.Directory

AVAILABLE

Functional Diagrams

Pin Configurations appear at end of data sheet.

Functional Diagrams continued at end of data sheet.

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at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

FEATURES

 1024 bits Electrically Programmable Read

Only Memory (EPROM) communicates with

the economy of one signal plus ground

 Unique, factory-lasered and tested 64-bit

registration number (8-bit family code + 48-

bit serial number + 8-bit CRC tester) assures

absolute traceability because no two parts are

alike

 Built-in multidrop controller ensures

compatibility with other MicroLAN products

 EPROM partitioned into four 256-bit pages

for randomly accessing packetized data

 Each memory page can be permanently

write-protected to prevent tampering

 Device is an “add only” memory where

additional data can be programmed into

EPROM without disturbing existing data

 Architecture allows software to patch data by

superseding an old page in favor of a newly

programmed page

 Reduces control, address, data, power, and

programming signals to a single data pin

 Directly connects to a single port pin of a

microprocessor and communicates at up to

16.3 kbits per second

 8-bit family code specifies DS2502

communications requirements to reader

 Presence detector acknowledges when the

reader first applies voltage

 Low cost TO-92, SFN, or 8-pin SO, SOT-23

(3-pin), TSOC and flip chip surface mount

package

 Reads over a wide voltage range of 2.8V to

6.0V from -40°C to +85°C; programs at

11.5V to 12.0V from -40°C to +50°C

PIN ASSIGNMENT

1 2

09rrd

Flip Chip, Top View

with Laser Mark,

Contacts Not Visible.

“rrd” = Revision/Date

1 = DATA

2 = GND

SFN (APPROX. 6.0mm x 6.0mm x 0.9mm)

BOTTOM VIEW

SIDE VIEW

1 2

SFN PINOUT:

PIN 1: IO

PIN 2: GND

NOTE: THE SFN PACKAGE IS QUALIFIED FOR ELECTRO-MECHANICAL

CONTACT APPLICATIONS ONLY, NOT FOR SOLDERING. FOR MORE

INFORMATION, REFER TO APPLICATION NOTE 4132: ATTACHMENT

METHODS FOR THE ELECTRO-MECHANICAL SFN PACKAGE.

DATA

TOP VIEW

TSOC PACKAGE

GND

DATA

GND

8-PIN SO (150 MIL)

DS2502

1Kb Add-Only Memory

GND

DATA

BOTTOM VIEW

TO-92

DS2502

SOT-23 Package

Top View

1 2

09rr

1 = DATA; 2, 3 = GND

“rr” = Revision

19-5075; Rev 12/11

DS2502

ORDERING INFORMATION

PART

TEMP RANGE

PIN-PACKAGE

DS2502+

-40°C to +85°C

3 TO-92 (straight leads)

DS2502+T&R

-40°C to +85°C

3 TO-92 (formed leads, 2k pieces)

DS2502G+T&R

-40°C to +85°C

2 SFN (2.5k pieces)

DS2502P+

-40°C to +85°C

6 TSOC

DS2502P+T&R

-40°C to +85°C

6 TSOC (4k pieces)

DS2502R+T&R

-40°C to +85°C

3 SOT-23 (3k pieces)

DS2502S+

-40°C to +85°C

8 SO

DS2502S+T&R

-40°C to +85°C

8 SO (2.5k pieces)

DS2502X1

-40°C to +85°C

2 Flip Chip (10k pieces)

+Denotes a lead(Pb)-free/RoHS-compliant package.

T&R = Tape and reel.

DESCRIPTION

The DS2502 1Kb Add-Only Memory identifies and stores relevant information about the product to

which it is associated. This lot- or product-specific information can be accessed with minimal interface-

for example, a single port pin of a microcontroller. The DS2502 consists of a factory-lasered registration

number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (09h) plus

1Kb of EPROM which is user-programmable. The power to program and read the DS2502 is derived

entirely from the 1-Wire communication line.

Data is transferred serially via the 1-Wire protocol which requires only a single data lead and a ground

return. The entire device can be programmed and then write-protected if desired. Alternatively, the part

may be programmed multiple times with new data being appended to, but not overwriting, existing data

with each subsequent programming of the device. Note: Individual bits can be changed only from a

logical 1 to a logical 0, never from a logical 0 to a logical 1. A provision is also included for indicating

that a certain page or pages of data are no longer valid and have been replaced with new or updated data

that is now residing at an alternate page address. This page address redirection allows software to patch

data and enhance the flexibility of the device as a stand-alone database. The 48-bit serial number that is

factory-lasered into each DS2502 provides a guaranteed unique identity which allows for absolute

traceability. The familiar TO-92 or SOIC or TSOC packages provide a compact enclosure that allows

standard assembly equipment to handle the device easily for attachment to printed circuit boards or

wiring. Typical applications include storage of calibration constants, maintenance records, asset tracking,

product revision status, and access codes.

OVERVIEW

The block diagram in Figure 1 shows the relationships between the major control and memory sections of

the DS2502. The DS2502 has three main data components: 1) 64-bit lasered ROM, 2) 1024-bit EPROM,

and 3) EPROM Status Bytes. The device derives its power for read operations entirely from the 1-Wire

communication line by storing energy on an internal capacitor during periods of time when the signal line

is high and continues to operate off of this “parasite” power source during the low times of the 1-Wire

line until it returns high to replenish the parasite (capacitor) supply. During programming, 1-Wire

communication occurs at normal voltage levels and then is pulsed momentarily to the programming

voltage to cause the selected EPROM bits to be programmed. The 1-Wire line must be able to provide 12

volts and 10 milliamperes to adequately program the EPROM portions of the part. Whenever

programming voltages are present on the 1-Wire line a special high voltage detect circuit within the

DS2502 generates an internal logic signal to indicate this condition. The hierarchical structure of the 1-

Wire protocol is shown in Figure 2. The bus master must first provide one of the six ROM Function

Commands, 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM. These commands operate on

the 64-bit lasered ROM portion of each device and can singulate a specific device if many are present on

1-Wire is a registered trademark of Maxim Integrated Products, Inc.

DS2502

the 1-Wire line as well as indicate to the bus master how many and what types of devices are present. The

protocol required for these ROM Function Commands is described in Figure 9. After a ROM Function

Command is successfully executed, the memory functions that operate on the EPROM portions of the

DS2502 become accessible and the bus master may issue any one of the five Memory Function

Commands specific to the DS2502 to read or program the various data fields. The protocol for these

Memory Function Commands is described in Figure 5. All data is read and written least significant bit

first.

64-BIT LASERED ROM

Each DS2502 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.

The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (See Figure 3).

The 64-bit ROM and ROM Function Control section allow the DS2502 to operate as a 1-Wire device and

follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The memory functions required

to read and program the EPROM sections of the DS2502 are not accessible until the ROM function

protocol has been satisfied. This protocol is described in the ROM functions flow chart (Figure 9). The 1-

Wire bus master must first provide one of four ROM function commands: 1) Read ROM, 2) Match ROM,

3) Search ROM, or 4) Skip ROM. After a ROM function sequence has been successfully executed, the

bus master may then provide any one of the memory function commands specific to the DS2502 (Figure

6).

The 1-Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Figure 4

shows a hardware implementation of this CRC generator. Additional information about the Maxim

1-Wire Cyclic Redundancy Check is available in Application Note 27. The shift register acting as the

CRC accumulator is initialized to 0. Then starting with the least significant bit of the family code, 1 bit at

a time is shifted in. After the 8th bit of the family code has been entered, then the serial number is

entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC

value. Shifting in the 8 bits of CRC should return the shift register to all 0s.

DS2502 BLOCK DIAGRAM Figure 1

PARASITE POWER

DATA

1-WIRE BUS

64-BIT LASERED

ROM

1-WIRE FUNCTION

CONTROL

PROGRAM

VOLTAGE

DETECT

MEMORY

FUNCTION

CONTROL

8-BIT

SCRATCHPAD

8-BIT CRC

GENERATOR

1024-BIT EPROM

(4 PAGES OF 32 BYTES)

STATUS BYTES

EPROM

DS2502

HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2

64-BIT LASERED ROM Figure 3

8–Bit CRC Code

48–Bit Serial Number

8–Bit Family Code (09h)

MSB

LSB

MSB

LSB

MSB

LSB

1-WIRE CRC GENERATOR Figure 4

DS2502

1024-BITS EPROM

The memory map in Figure 5 shows the 1024-bit EPROM section of the DS2502 which is configured as

four pages of 32 bytes each. The 8-bit scratchpad is an additional register that acts as a buffer when

programming the memory. Data is first written to the scratchpad and then verified by reading an 8-bit

CRC from the DS2502 that confirms proper receipt of the data. If the buffer contents are correct, a

programming voltage should be applied and the byte of data will be written into the selected address in

memory. This process ensures data integrity when programming the memory. The details for reading and

programming the 1024-bit EPROM portion of the DS2502 are given in the Memory Function Commands

section.

EPROM STATUS BYTES

In addition to the 1024 bits of data memory the DS2502 provides 64 bits of Status Memory accessible

with separate commands.

The EPROM Status Bytes can be read or programmed to indicate various conditions to the software

interrogating the DS2502. The first byte of the EPROM Status Memory contain the Write Protect Page

bits which inhibit programming of the corresponding page in the 1024-bit main memory area if the

appropriate write protection bit is programmed. Once a bit has been programmed in the Write Protect

Page byte, the entire 32-byte page that corresponds to that bit can no longer be altered but may still be

read.

The next 4 bytes of the EPROM Status Memory contain the Page Address Redirection Bytes, which

indicate if one or more of the pages of data in the 1024-bit EPROM section have been invalidated and

redirected to the page address contained in the appropriate redirection byte. The hardware of the DS2502

makes no decisions based on the contents of the Page Address Redirection Bytes. These additional bytes

of Status EPROM technology, bits within a page can be changed from a logical 1 to a logical 0 by

programming, but cannot be changed back. Therefore, it is not possible to simply rewrite a page if the

data requires changing or updating, but with space permitting, an entire page of data can be redirected to

another page within the DS2502 by writing the one’s complement of the new page address into the Page

Address Redirection Byte that corresponds to the original (replaced) page.

This architecture allows the user’s software to make a “data patch” to the EPROM by indicating that a

particular page or pages should be replaced with those indicated in the Page Address Redirection Bytes.

If a Page Address Redirection Byte has an FFH value, the data in the main memory that corresponds to

that page is valid. If a Page Address Redirection Byte has some other hex value, the data in the page

corresponding to that redirection byte is invalid, and the valid data can now be found at the one’s

complement of the page address indicated by the hex value stored in the associated Page Address

Redirection Byte. A value of FDH in the redirection byte for page 1, for example, would indicate that the

updated data is now in page 2. The details for reading and programming the EPROM status memory

portion of the DS2502 are given in the Memory Function Commands section.

MEMORY FUNCTION COMMANDS

The “Memory Function Flow Chart” (Figure 6) describes the protocols necessary for accessing the

various data fields within the DS2502. The Memory Function Control section, 8-bit scratchpad, and the

Program Voltage Detect circuit combine to interpret the commands issued by the bus master and create

the correct control signals within the device. A 3-byte protocol is issued by the bus master. It is comprised

of a command byte to determine the type of operation and two address bytes to determine the specific

starting byte location within a data field. The command byte indicates if the device is to be read or

DS2502

written. Writing data involves not only issuing the correct command sequence by also providing a 12-volt

programming voltage at the appropriate times. To execute a write sequence, a byte of data is first loaded

into the scratchpad and then programmed into the selected address. Write sequences always occur a byte

at a time. To execute a read sequence, the starting address is issued by the bus master and data is read

from the part beginning at that initial location and continuing to the end of the selected data field or until

a reset sequence is issued. All bits transferred to the DS2502 and received back by the bus master are sent

least significant bit first.

DS2502 MEMORY MAP Figure 5

DS2502

MEMORY FUNCTION FLOW CHART Figure 6

DS2502

MEMORY FUNCTION FLOW CHART Figure 6 (cont’d)

LEGEND:

DECISION MADE

BY THE MASTER

DECISION MADE

BY DS2502

DS2502

MEMORY FUNCTION FLOW CHART Figure 6 (cont’d)

DS2502

READ MEMORY [F0h]

The Read Memory command is used to read data from the 1024-bit EPROM data field. The bus master

follows the command byte with a 2-byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting

byte location within the data field. An 8-bit CRC of the command byte and address bytes is computed by

the DS2502 and read back by the bus master to confirm that the correct command word and starting

address were received. If the CRC read by the bus master is incorrect, a reset pulse must be issued and the

entire sequence must be repeated. If the CRC received by the bus master is correct, the bus master issues

read time slots and receives data from the DS2502 starting at the initial address and continuing until the

end of the 1024-bit data field is reached or until a reset pulse is issued. If reading occurs through the end

of memory space, the bus master may issue eight additional read time slots and the DS2502 will respond

with a 8-bit CRC of all data bytes read from the initial starting byte through the last byte of memory.

After the CRC is received by the bus master, any subsequent read time slots will appear as logical 1s until

a reset pulse is issued. Any reads ended by a reset pulse prior to reaching the end of memory will not have

the 8-bit CRC available.

Typically a 16-bit CRC would be stored with each page of data to ensure rapid, error-free data transfers

that eliminate having to read a page multiple times to determine if the received data is correct or not. (See

Application Note 114 for the recommended file structure.) If CRC values are imbedded within the data, a

reset pulse may be issued at the end of memory space during a Read Memory command.

READ STATUS [AAh]

The Read Status command is used to read data from the EPROM Status data field. The bus master

follows the command byte with a 2-byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting

byte location within the data field. An 8-bit CRC of the command byte and address bytes is computed by

the DS2502 and read back by the bus master to confirm that the correct command word and starting

address were received. If the CRC read by the bus master is incorrect, a reset pulse must be issued and the

entire sequence must be repeated. If the CRC received by the bus master is correct, the bus master issues

read time slots and receives data from the DS2502 starting at the supplied address and continuing until

the end of the EPROM Status data field is reached. At that point the bus master will receive an 8-bit CRC

that is the result of shifting into the CRC generator all of the data bytes from the initial starting byte

through the final factory-programmed byte that contains the 00h value.

This feature is provided since the EPROM Status information may change over time making it impossible

to program the data once and include an accompanying CRC that will always be valid. Therefore, the

Read Status command supplies a 8-bit CRC that is based on and always is consistent with the current data

stored in the EPROM Status data field.

After the 8-bit CRC is read, the bus master will receive logical 1s from the DS2502 until a reset pulse is

issued. The Read Status command sequence can be ended at any point by issuing a reset pulse.

READ DATA/GENERATE 8-BIT CRC [C3h]

The Read Data/Generate 8-bit CRC command is used to read data from the 1024-bit EPROM data field.

The bus master follows the command byte with a 2-byte address (TA1=(T7:T0), TA2=(T15:T8)) that

indicates a starting byte location within the data field. An 8-bit CRC of the command byte and address

bytes is computed by the DS2502 and read back by the bus master to confirm that the correct command

word and starting address were received. If the CRC read by the bus master is incorrect, a reset pulse

must be issued and the entire sequence must be repeated. If the CRC received by the bus master is

correct, the bus master issues read time slots and receives data from the DS2502 starting at the initial

address and continuing until the end of a 32-byte page is reached. At that point the bus master will send

DS2502

eight additional read time slots and receive an 8-bit CRC that is the result of shifting into the CRC

generator all of the data bytes from the initial starting byte to the last byte of the current page. Once the 8-

bit CRC has been received, data is again read from the 1024-bit EPROM data field starting at the next

page. This sequence will continue until the final page and its accompanying CRC are read by the bus

master. Thus each page of data can be considered to be 33 bytes long: the 32 bytes of user-programmed

EPROM data and an 8-bit CRC that gets generated automatically at the end of each page.

This type of read differs from the Read Memory command which simple reads each page until the end of

address space is reached. The Read Memory command only generates an 8-bit CRC at the end of memory

space that often might be ignored, since in many applications the user would store a 16-bit CRC with the

data itself in each page of the 1024-bit EPROM data field at the time the page was programmed.

The Read Data/Generate 8-bit CRC command provides and alternate read capability for applications that

are “bit-oriented” rather than “page-oriented” where the 1024-bit EPROM information may change over

time within a page boundary making it impossible to program the page once and include an

accompanying CRC that will always be valid. Therefore, the Read Data/Generate 8-bit CRC command

concludes each page with the DS2502 generating and supplying an 8-bit CRC that is based on and

therefore is always consistent with the current data stored in each page of the 1024-bit EPROM data field.

After the 8-bit CRC of the last page is read, the bus master will receive logical 1s from the DS2502 until a

reset pulse is issued. The Read Data/Generate 8-Bit CRC command sequence can be exited at any point

by issuing a reset pulse.

WRITE MEMORY [0Fh]

The Write Memory command is used to program the 1024–bit EPROM data field. The bus master will

follow the command byte with a 2-byte starting address (TA1 = (T7:T0), TA2 = (T15:T8)) and a byte of

data (D7:D0). An 8-bit CRC of the command byte, address bytes, and data byte is computed by the

DS2502 and read back by the bus master to confirm that the correct command word, starting address, and

data byte were received.

The highest starting address within the DS2502 is 007FH. If the bus master sends a starting address

higher than this, the nine 9 most significant address bits are set to 0 by the internal circuitry of the chip.

This will result in a mismatch between the CRC calculated by the DS2502 and the CRC calculated by the

bus master, indicating an error condition.

If the CRC read by the bus master is incorrect, a reset pulse must be issued and the entire sequence must

be repeated. If the CRC received by the bus master is correct, a programming pulse (12 volts on the 1-

Wire bus for 480 µs) is issued by the bus master. Prior to programming, the entire unprogrammed 1024-

bit EPROM data field will appear as logical 1s. For each bit in the data byte provided by the bus master

that is set to a logical 0, the corresponding bit in the selected byte of the 1024-bit EPROM will be

programmed to a logical 0 after the programming pulse has been applied at that byte location.

After the 480 µs programming pulse is applied and the data line returns to a 5-volt level, the bus master

issues eight read time slots to verify that the appropriate bits have been programmed. The DS2502

responds with the data from the selected EPROM address sent least significant bit first. This byte contains

the logical AND of all bytes written to this EPROM data address. If the EPROM data byte contains 1s in

bit positions where the byte issued by the master contains 0s, a reset pulse should be issued and the

current byte address should be programmed again. If the DS2502 EPROM data byte contains 0s in the

same bit positions as the data byte, the programming was successful and the DS2502 will automatically

increment its address counter to select the next byte in the 1024-bit EPROM data field. The least

DS2502

significant byte of the new two-byte address will also be loaded into the 8-bit CRC generator as a starting

value. The bus master will issue the next byte of data using eight write time slots.

As the DS2502 receives this byte of data into the scratchpad, it also shifts the data into the CRC generator

that has been preloaded with the LSB of the current address; the result is an 8-bit CRC of the new data

byte and the LSB of the new address. After supplying the data byte, the bus master will read this 8-bit

CRC from the DS2502 with eight read time slots to confirm that the address incremented properly and the

data byte was received correctly. If the CRC is incorrect, a reset pulse must be issued and the Write

Memory command sequence must be restarted. If the CRC is correct, the bus master will issue a

programming pulse and the selected byte in memory will be programmed.

Note that the initial pass through the Write Memory flow chart will generate an 8-bit CRC value that is

the result of shifting the command byte into the CRC generator, followed by the two address bytes, and

finally the data byte. Subsequent passes through the Write Memory flow chart due to the DS2502

automatically incrementing its address counter will generate an 8-bit CRC that is the result of loading (not

shifting) the LSB of the new (incremented) address into the CRC generator and then shifting in the new

data byte.

For both of these cases, the decision to continue (to apply a program pulse to the DS2502) is made

entirely by the bus master, since the DS2502 will not be able to determine if the 8-bit CRC calculated by

the bus master agrees with the 8-bit CRC calculated by the DS2502. If an incorrect CRC is ignored and a

program pulse is applied by the bus master, incorrect programming could occur within the DS2502. Also

note that the DS2502 will always increment its internal address counter after the receipt of the eight read

time slots used to confirm the programming of the selected EPROM byte. The decision to continue is

again made entirely by the bus master, therefore if the EPROM data byte does not match the supplied

data byte does not match the supplied data byte but the master but the master continues with the Write

Memory command, incorrect programming could occur within the DS2502. The Write Memory

command sequence can be exited at any point by issuing a reset pulse.

WRITE STATUS [55h]

The Write Status command is used to program the EPROM status data field. The bus master will follow

the command byte with a 2-byte starting address (TA1=(T7:T0), TA2=(T15:T8)) and a byte of status data

(D7:D0). An 8-bit CRC of the command byte, address bytes, and data byte is computed by the DS2502

and read back by the bus master to confirm that the correct command word, starting address, and data

byte were received.

If the CRC read by the bus master is incorrect, a reset pulse must be issued and the entire sequence must

be repeated. If the CRC received by the bus master is correct, a programming pulse (12 volts on the 1-

Wire bus for 480 µs) is issued by the bus master. Prior to programming, the first 7 bytes of the EPROM

Status data field will appear as logical 1s. For each bit in the data byte provided by the bus master that is

set to a logical 0, the corresponding bit in the selected byte of the EPROM Status data field will be

programmed to a logical 0 after the programming pulse has been applied at the byte location. The 8th

byte of the EPROM Status Byte data field is factory-programmed to contain 00h.

After the 480 µs programming pulse is applied and the data line returns to a 5-volt level, the bus master

issues eight read time slots to verify that the appropriate bits have been programmed. The DS2502

responds with the data from the selected EPROM Status address sent least significant bit first. This byte

contains the logical AND of all bytes written to this EPROM Status Byte address. If the EPROM Status

Byte contains 1s in bit positions where the byte issued by the master contained 0s, a reset pulse should be

DS2502

issued and the current byte address should be programmed again. If the DS2502 EPROM Status Byte

contains 0s in the same bit positions as the data byte, the programming was successful and the DS2502

will automatically increment its address counter to select the next byte in the EPROM Status data field.

The least significant byte of the new 2-byte address will also be loaded into the 8-bit CRC generator as a

starting value. The bus master will issue the next byte of data using eight write time slots.

As the DS2502 receives this byte of data into the scratchpad, it also shifts the data into the CRC generator

that has been preloaded with the LSB of the current address and the result is an 8-bit CRC of the new data

byte and the LSB of the new address. After supplying the data byte, the bus master will read this 8-bit

CRC from the DS2502 with eight read time slots to confirm that the address incremented properly and the

data byte was received correctly. If the CRC is incorrect, a reset pulse must be issued and the Write Status

command sequence must be restarted. If the CRC is correct, the bus master will issue a programming

pulse and the selected byte in memory will be programmed.

Note that the initial pass through the Write Status flow chart will generate an 8-bit CRC value that is the

result of shifting the command byte into the CRC generator, followed by the 2 address bytes, and finally

the data byte. Subsequent passes through the Write Status flow chart due to the DS2502 automatically

incrementing its address counter will generate an 8-bit CRC that is the result of loading (not shifting) the

LSB of the new (incremented) address into the CRC generator and then shifting in the new data byte.

For both of these cases, the decision to continue (to apply a program pulse to the DS2502) is made

entirely by the bus master, since the DS2502 will not be able to determine if the 8-bit CRC calculated by

the bus master agrees with the 8-bit CRC calculated by the DS2502. If an incorrect CRC is ignored and a

program pulse is applied by the bus master, incorrect programming could occur within the DS2502. Also

note that the DS2502 will always increment its internal address counter after the receipt of the eight read

time slots used to confirm the programming of the selected EPROM byte. The decision to continue is

again made entirely by the bus master, therefore if the EPROM data byte does not match the supplied

data byte but the master continues with the Write Status command, incorrect programming could occur

within the DS2502. The Write Status command sequence can be ended at any point by issuing a reset

pulse.

1-Wire BUS SYSTEM

The 1-Wire bus is a system which has a single bus master and one or more slaves. In all instances, the

DS2502 is a slave device. The bus master is typically a microcontroller. The discussion of this bus

system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire

signaling (signal type and timing). A 1-Wire protocol defines bus transactions in terms of the bus state

during specified time slots that are initiated on the falling edge of sync pulses from the bus master.

Hardware Configuration

The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to

drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have an

open drain connection or three-state outputs. The DS2502 is an open drain part with an internal circuit

equivalent to that shown in Figure 7. The bus master can be the same equivalent circuit. If a bi-directional

pin is not available, separate output and input pins can be tied together.

The bus master requires a pullup resistor at the master end of the bus, with the bus master circuit

equivalent to the one shown in Figures 8a and 8b. The value of the pullup resistor should be

approximately 5 kΩ for short line lengths.

DS2502

A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At regular speed the 1-Wire bus

has a maximum data rate of 16.3 kbits per second. If the bus master is also required to perform

programming of the EPROM portions of the DS2502, a programming supply capable of delivering up to

10 milliamps at 12 volts for 480 µs is required. The idle state for the 1-Wire bus is high. If, for any

reason, a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to

resume. If this does not occur and the bus is left low for more than 120 µs, one or more of the devices on

the bus may be reset.

Transaction Sequence

The sequence for accessing the DS2502 via the 1-Wire port is as follows:

 Initialization

 ROM Function Command

 Memory Function Command

 Read/Write Memory/Status

INITIALIZATION

All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence

consists of a reset pulse transmitted by the bus master followed by a presence pulse(s) transmitted by the

slave(s).

The presence pulse lets the bus master know that the DS2502 is on the bus and is ready to operate. For

more details, see the “1-Wire Signaling” section.

ROM FUNCTION COMMANDS

Once the bus master has detected a presence, it can issue one of the six ROM function commands. All

ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure

9):

Read ROM [33h]

This command allows the bus master to read the DS2502’s 8-bit family code, unique 48-bit serial

number, and 8-bit CRC. This command can be used only if there is a single DS2502 on the bus. If more

than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same

time (open drain will produce a wired-AND result).

Match ROM [55h]

The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a

specific DS2502 on a multidrop bus. Only the DS2502 that exactly matches the 64-bit ROM sequence

will respond to the subsequent memory function command. All slaves that do not match the 64-bit ROM

sequence will wait for a reset pulse. This command can be used with a single or multiple devices on the

bus.

DS2502

DS2502 EQUIVALENT CIRCUIT Figure 7

BUS MASTER CIRCUIT Figure 8

DS2502

ROM FUNCTIONS FLOW CHART Figure 9

DS2502

Skip ROM [CCh]

This command can save time in a single-drop bus system by allowing the bus master to access the

memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus

and a read command is issued following the Skip ROM command, data collision will occur on the bus as

multiple slaves transmit simultaneously (open drain pulldowns will produce a wired-AND result).

Search ROM [F0h]

When a system is initially brought up, the bus master might not know the number of devices on the 1-

Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process

of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process

is the repetition of a simple, three-step routine: read a bit, read the complement of the bit, then write the

desired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM.

After one complete pass, the bus master knows the contents of the ROM in one device. The remaining

number of devices and their ROM codes may be identified by additional passes. See Application Note

187 for a comprehensive discussion of a ROM search, including an actual example.

1-Wire Signaling

The DS2502 requires strict protocols to ensure data integrity. The protocol consists of five types of

signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, Read Data

and Program Pulse. All these signals except presence pulse are initiated by the bus master. The

initialization sequence required to begin any communication with the DS2502 is shown in Figure 10. A

Reset Pulse followed by a Presence Pulse indicates the DS2502 is ready to accept a ROM command. The

bus master transmits (TX) a reset pulse (tRSTL, minimum 480 µs). The bus master then releases the line

and goes into receive mode (RX). The 1-Wire bus is pulled to a high state via the pullup resistor. After

detecting the rising edge on the data pin, the DS2502 waits (tPDH, 15-60 µs) and then transmits the

presence pulse (tPDL, 60-240 µs).

Read/Write Time Slots

The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by the

master driving the data line low. The falling edge of the data line synchronizes the DS2502 to the master

by triggering a delay circuit in the DS2502. During write time slots, the delay circuit determines when the

DS2502 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit

determines how long the DS2502 will hold the data line low overriding the “1” generated by the master.

If the data bit is a 1, the device will leave the read data time slot unchanged.

PROGRAM PULSE

To copy data from the 8-bit scratchpad to the 1024-bit EPROM Memory or Status Memory, a program

pulse of 12 volts is applied to the data line after the bus master has confirmed that the CRC for the current

byte is correct. During programming, the bus master controls the transition from a state where the data

line is idling high via the pullup resistor to a state where the data line is actively driven to a programming

voltage of 12 volts providing a minimum of 10 mA of current to the DS2502. This programming voltage

(Figure 12) should be applied for 480 µs, after which the bus master returns the data line to an idle high

state controlled by the pullup resistor. Note that due to the high-voltage programming requirements for

any 1-Wire EPROM device, it is not possible to multidrop non-EPROM based 1-Wire devices with the

DS2502 during programming. An internal diode within the non-EPROM based 1-Wire devices will

attempt to clamp the data line at approximately 8 volts and could potentially damage these devices.

DS2502

CRC GENERATION

The DS2502 has an 8-bit CRC stored in the most significant byte of the 64-bit ROM. The bus master can

compute a CRC value from the first 56 bits of the 64-bit ROM and compare it to the value stored within

the DS2502 to determine if the ROM data has been received error-free by the bus master. The equivalent

polynomial function of this CRC is: X8 + X5 + X4 +1.

Under certain conditions, the DS2502 also generates an 8-bit CRC value using the same polynomial

function shown above and provides this value to the bus master to validate the transfer of command,

address, and data bytes from the bus master to the DS2502. The Memory Function Flow Chart of Figure

6 indicates that the DS2502 computes an 8-bit CRC for the command, address, and data bytes received

for the Write Memory and the Write Status commands and then outputs this value to the bus master to

confirm proper transfer. Similarly the DS2502 computes an 8-bit CRC for the command and address

bytes received from the bus master for the Read Memory, Read Status, and Read Data/Generate 8-Bit

CRC commands to confirm that these bytes have been received correctly. The CRC generator on the

DS2502 is also used to provide verification of error-free data transfer as each page of data from the 1024-

bit EPROM is sent to the bus master during a Read Data/Generate 8-Bit CRC command, and for the 8

bytes of information in the status memory field.

In each case where a CRC is used for data transfer validation, the bus master must calculate a CRC value

using the polynomial function given above and compare the calculated value to either the 8-bit CRC

value stored in the 64-bit ROM portion of the DS2502 (for ROM reads) or the 8-bit CRC value computed

within the DS2502. The comparison of CRC values and decision to continue with an operation are

determined entirely by the bus master. There is no circuitry on the DS2502 that prevents a command

sequence from proceeding if the CRC stored in or calculated by the DS2502 does not match the value

generated by the bus master. Proper use of the CRC as outlined in the flow chart of Figure 6 can result in

a communication channel with a very high level of integrity. For more details on generating CRC values

including example implementations in both hardware and software, see Application Note 27.

INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 10

RESISTOR

MASTER

DS2502

480µs ≤ t

RSTL

< 960µs

480µs ≤ tRSTH < ∞ (includes recovery time)

15µs ≤ tPDH < 60µs

60µs ≤ tPDL < 240µs

DS2502

READ/WRITE TIMING DIAGRAM Figure 11

Write-one Time Slot

60 µs ≤ tSLOT < 120 µs

1 µs ≤ tLOW1 < 15 µs

1 µs ≤ tREC < ∞

Write-zero Time Slot

60 µs ≤ tLOW0 < tSLOT < 120 µs

1 µs ≤ tREC < ∞

Read-data Time Slot

60 µs ≤ tSLOT < 120 µs

1 µs ≤ tLOWR < 15 µs

0 ≤ tRELEASE < 45 µs

1 µs ≤ tREC < ∞

tRDV = 15 µs

tSU < 1 µs

DS2502 SAMPLING WINDOW

RESISTOR

MASTER

DS2502

PROGRAM PULSE TIMING DIAGRAM Figure 12

DS2502

ABSOLUTE MAXIMUM RATINGS

Voltage on any Pin Relative to Ground -0.5V to +12.0V

Operating Temperature -40°C to +85°C

Storage Temperature -55°C to +125°C

Lead Temperature (TO-92, TSOC, SOT23-3, SOIC only, soldering 10s) +300°C

Soldering Temperature (reflow)

TO-92 +250°C

TSOC, SOT-23, SOIC +260°C

Flip Chip +240°C

SFN Refer to Application Note 4132: Attachment

methods for the electro-mechanical SFN package.

This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the

operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of

time may affect reliability.

DC ELECTRICAL CHARACTERISTICS (TA = -40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Pullup Voltage

VPUP

2.8

1, 2

Logic 1

VIH

2.2

1, 6

Logic 0

VIL

-0.3

+0.8

1, 11

Output Logic Low @ 4 mA

VOL

0.4

Input Load Current

µA

Operating Charge

QOP

7, 8

Programming Voltage @ 10 mA

VPP

11.5

12.0

Valid EPROM Read Voltage

VEPR

2.8

6.0

CAPACITANCE (TA =25°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Data (1-Wire)

CIN/OUT

800

AC ELECTRICAL CHARACTERISTICS (TA = -40°C to +85°C)

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

NOTES

Time Slot

tSLOT

120

µs

Write 1 Low Time

tLOW1

µs

Write 0 Low Time

tLOW0

120

µs

Read Data Valid

tRDV

exactly 15

µs

Release Time

tRELEASE

µs

Read Data Setup

tSU

µs

Recovery Time

tREC

µs

Reset Time High

tRSTH

480

µs

Reset Time Low

tRSTL

480

960

µs

Presence Detect High

tPDH

µs

Presence Detect Low

tPDL

240

µs

Delay to Program

tDP

µs

Delay to Verify

tDV

µs

Program Pulse Width

tPP

480

5000

µs

10, 12

Program Voltage Rise Time

tRP

0.5

5.0

µs

Program Voltage Fall Time

tFP

0.5

5.0

µs

DS2502

NOTES:

1. All voltages are referenced to ground.

2. VPUP = external pullup voltage.

3. Input load is to ground.

4. An additional reset or communication sequence cannot begin until the reset high time has expired.

5. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is

guaranteed to be valid within 1 µs of this falling edge and will remain valid for 14 µs minimum. (15

µs total from falling edge on 1-Wire bus.)

6. VIH is a function of the external pullup resistor and the pull-up voltage.

7. 30 nanocoulombs per 72 time slots @ 5.0V.

8. At VCC=5.0V with a 5 kΩ pullup to VCC and a maximum time slot of 120 µs.

9. Capacitance on the data pin could be 800 pF when power is first applied. If a 5 kΩ resistor is used to

pullup the data line to VCC, 5 µs after power has been applied the parasite capacitance will not affect

normal communications.

10. Maximum 1-Wire voltage for programming parameters is 11.5V to 12.0V; temperature range is -40°C

to +50°C.

11. Under certain low-voltage conditions VILMAX may have to be reduced to as much as 0.5V to always

guarantee a presence pulse.

12. The accumulative duration of the programming pulses for each address must not exceed 5 ms.

13. IC operation and 1-wire communication is valid at VPUP=2.5V or higher, but EPROM data read is

only valid when VPUP=2.8V or higher.

14. Reset low pulse on DQ must be preceded by a valid tREC recovery time above the minimum VPUP

voltage of 2.5V.

DS2502

PACKAGE INFORMATION

For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages.

Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a

different suffix character, but the drawing pertains to the package regardless of RoHS status.

PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.

3 TO-92 (straight leads)

Q3+1

21-0248

—

3 TO-92 (formed leads) Q3+4 21-0250 —

2 SFN G266N+1 21-0390 —

6 TSOC D6+1 21-0382 90-0321

3 SOT-23 U3+5 21-0051 90-0179

8 SO S8+2 21-0041 90-0096

2 Flip Chip BF211-2 21-0379 Refer to 21-0379

DS2502

REVISION HISTORY

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

102199

Conversion to new template.

all

030806

SOT-23 package added, lead (Pb)-free part numbers added.

1, 2

032307

Flip chip package added.

1, 2

071107

Note added that TO-92 tape & reel has formed leads.

12/09

Added note to Figure 10 that changed t

RSTL

to 960µs maximum.

Added V

EPR

specification.

Changed tRSTL to 960µs maximum.

Added notes 13 and 14 to Electrical Characteristics table.

12/11

Added SFN package, cleaned up ordering information; typo corrections.

1, 2, 5, 9, 11

Updated lead temperature and soldering information.

Moved V

PUP

from Electrical Characteristics table header to table body,

deleted VOH from the Electrical Characteristics table.

Added Package Information section; extended Revision History.

23, 24

Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.

Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical

Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.