MAXSMBus - Maxim Integrated Products, Inc.

___MAXSMBus Functionality Check

Follow these steps to verify that the MAXSMBus inter-

face board is functioning properly. All necessary soft-

ware is supplied on a disk with the companion EV kit.

Instructions for operating the software are included in

the EV kit manual.

1) Connect a +9V DC supply (+7V minimum, +20V

maximum) to the MAXSMBus interface board at the

terminals labeled “POS9” and “GND” in the lower

left corner of the board.

2) Use a digital voltmeter to verify that the oval pad

labeled “POS5” is +5V (+4.75V minimum, +5.25V

maximum). Also verify that the pads labeled

“SBDAT1,” “SBCLK1,” “SBSUS1,” “ALERT1,” and

“ALERT2” are above +4V.

3) If these DC voltages are correct, MAXSMBus pass-

es the functionality test.

_______________Detailed Description

The MAXSMBus interface board provides all of the

interface signals necessary to interface an IBM PC-

compatible computer with an SMBus-compliant device.

A DB25 right-angle plug connects to the computer

(Table 1). The companion board plugs into a 20-pin

dual-row right-angle header at the edge of the board

(Table 2). Alternatively, connection can be made by

soldering wires to the oval pads as appropriate. This

allows the companion board to be placed in an environ-

mental chamber for evaluation over temperature.

Refer to the documentation of the companion Maxim EV

kit for quick start and operating instructions.

________________General Description

MAXSMBus is an interface between an IBM-compatible

PC and System Management Bus (SMBus)™-

compatible serial-interface devices such as tempera-

ture monitors, voltage regulators, or A/D converters

(ADCs). The MAXSMBus interface board is connected

between the PC parallel port and the device under test,

converting parallel data into two-wire, open-drain serial

data. The board is provided for use with selected

Maxim products and is not intended to replace com-

mercially available SMBus hardware. MAXSMBus is

shipped with a companion EV kit board, including all

relevant software.

____________________________Features

♦SMBus-Compatible Two-Wire Interface

♦SMBus Suspend Output

♦Two SMBus Alert Inputs

♦Overvoltage Fault Protection

♦PC Parallel Port Interface

Evaluates: MAXSMBus

Two-Wire Interface Board

________________________________________________________________ Maxim Integrated Products 1

19-1306; Rev 0; 3/98

QTY DESCRIPTION

C1, C2, C3 30.1µF ceramic capacitors

C4–C9 63.3µF, 25V tantalum capacitors

D1 11N5235B zener diode, 6.8V

D2 11N5229B zener diode, 4.3V

D3 11N4148 small signal diode

J1 1DB25 right angle plug

DESIGNATION

_______________Ordering Information

PART

MAXSMBus

BOARD TYPE

Companion Board for SMBus EV Kits

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.

For small orders, phone 408-737-7600 ext. 3468.

Maxim SMBus Interface Board

____________________________Component List

J2 1Not installed

P1 12 x 10 right angle male header

R1, R2, R3,

R10, R11 547kΩ, 5% resistors

R4–R7 4 4.7kΩ, 5% resistors

R8, R9 21kΩ, 5% resistors

U1 174HC05 hex open-collector inverter

U2 174HC04 hex inverter

U3 174HC08 quad AND gate

U4 174HC74 dual D flip-flop

U5 1+5V, 100mA regulator, LM78L05ACM

U6 1MAX865EUA (8 µMAX)

U7 1MAX367CWN (18 SO)

NONE 1 PC board

SMBus is a trademark of Intel Corp.

Evaluates: MAXSMBus

Two-Wire Interface Board

2 _______________________________________________________________________________________

SYMPTOMS CAUSE SOLUTION

Can’t Find the Interface Board Board not connected to

parallel printer port

Verify that the cable is a 25-pin parallel port I/O extension cable

with a plug on one end and a socket on the other end.

Verify that the cable is connected to a printer port, not a floppy

disk, SCSI, or serial communications port.

Clock or Data Stuck Low

Board is connected to cor-

rect port, but SMBus is not

functioning

Check power connections on the interface board.

Check clock and data signal connections.

Try operating the interface board without the companion Maxim

evaluation kit—this should cause the address-not-acknowledged

symptom described below.

Power Supply

The interface board is powered by a 78L05 linear regu-

lator. The companion board can draw about 20mA of

+5V power through the circuit protector. Companion

boards that require more power must provide their own

regulator. The unregulated input to the 78L05 is avail-

able on the right-angle header.

Fault Protection Circuitry

Overvoltage fault protection is provided by a MAX367

fault protector (U7). If any of the SMBus interface sig-

nals exceed the MAX367’s power supply rails, the

MAX367 increases its resistance to prevent damage to

the user’s computer. A MAX865 dual charge pump

(U6) and two zener diodes (D1 and D2) provide +7V

and -3V supplies to the MAX367, thus allowing 0V and

+5V signals to pass with a nominal resistance of 100Ω.

Bus Driving Circuitry

A 74HC05 open-drain inverter (U1) is used to pull down

the SMBus interface signals. The 74HC08 (U3),

74HC74 (U4), and 74HC04 (U2) buffer the signal to the

IBM PC and provide the capability to mask the ALERT

interrupts, detect an externally generated start condi-

tion, and capture data sent by an external bus master.

Interface connections are listed in Table 1 and Table 2.

Bus Monitoring Circuitry

Flip-flop U4A detects the start condition (falling edge of

SMBDATA when SMBCLK is high). Flip-flop U4B

detects the falling SMBCLK edge when enabled, and

U1F holds SMBCLK low until the software releases it.

To advance to the next data bit, the software uses U1A

to assert and then release SMBCLK. A logic high at the

input of U1A also resets flip-flop U4B. Because the IBM

PC parallel port has a limited number of inputs, the

start-detect circuit and the two alert inputs share a sin-

gle interrupt input. The source of the interrupt is distin-

guished using U3A, U3B, and U3C.

________________________________________________________Troubleshooting Guide

Address Not Acknowledged

SMBus is OK, but no

response at expected

SMBus address

Verify that the companion board is connected to the MAXSMBus

interface board.

Verify that the companion board is powered.

If the companion offers a choice of addresses, confirm that the soft-

ware and hardware addresses match. Some devices only read the

address select pins at device power-up.

Conflict with local printer

driver

Disable print manager in Windows printer control panel. Disable

printer driver.

Operating system conflict

1) Use computer with commercially available BIOS.

2) Make a bootable floppy disk, remove unnecessary device dri-

vers from A:config.sys, and boot system from floppy.

Erratic Operation

Evaluates: MAXSMBus

Two-Wire Interface Board

_______________________________________________________________________________________ 3

Table 1. DB25 Connector Signals

PIN NAME FUNCTION

1SPARE OUTPUT A Spare output

2SMBCLK_

OUT When high, drives SMBCLK signal low

3SMBDATA_

OUT When high, drives SMBDATA signal low

4SMBUS_OUT When high, drives SMBSUS signal low

5 LOOPBACK Loopback connection for port verification

6MASK_

ALERT1 When high, allows ALERT1 to trigger INT low

7MASK_

ALERT2 When high, allows ALERT2 to trigger INT low

8MASK_

START When high, allows a start condition to trigger INT low

9CAPTURE_ENABLE When high, enables slave / bus monitor circuitry. This circuit waits until SMBCLK

is pulled low, and then it holds SMBCLK until the software resets it.

10 INT Active low interrupt input

11 SMBDATA_

IN When high, indicates that SMBDATA is low

12 SMBCLK_

IN When high, indicates that SMBCLK is low

13 LOOPBACK Loopback connection for port verification

14 SPARE OUTPUT B Spare output

15 HOLDING_

CLOCK When low, indicates that interface board is holding SMBCLK low

16 UNUSED Not used

17 UNUSED Not used

18–25 GND Signal ground return

Evaluates: MAXSMBus

Two-Wire Interface Board

4 _______________________________________________________________________________________

Note: Odd-numbered pins are on the outer row. Even-numbered pins are on the inner row. All right-angle header signals pass through

the MAX367 circuit protector, except 20.

Table 2. Right-Angle Header P1 Signals

PIN NAME FUNCTION

1DUT +5V +5V at 20mA power supply to Maxim companion board

2GND Signal ground return

3DUT SDA SMBDATA interface signal

4GND Signal ground return

5GND Signal ground return

6GND Signal ground return

7DUT SCL SMBCLK interface signal

8GND Signal ground return

9DUTSMBSUS SMBSUS interface signal

10 GND Signal ground return

11 DUTSMBALERT Primary ALERT interface signal

12 GND Signal ground return

13 DUTALERT2 Secondary ALERT interface signal

14 GND Signal ground return

15 SPARE OUTPUT A Spare output from pin 1 of the DB25 connector

16 GND Signal ground return

17 SPARE OUTPUT B Spare output from pin 14 of the DB25 connector

18 GND Signal ground return

19 GND Signal ground return

20 RAW POWER Unregulated, unprotected power-supply input to MAXSMBus interface board

Evaluates: MAXSMBus

Two-Wire Interface Board

_______________________________________________________________________________________ 5

U1C

74HC04

74HC08 6

U2E U3A

J1–6 2

ALERT1ALERT1

R10

47k

R11

47k

+5V

ALERT1

MASK_ALERT1

U1D

74HC05

+5V

74HC05

INT

J1–10

74HC04

74HC08 8

47k

U2F

U2A

U3B

J1–7 5

ALERT2ALERT2

ALERT2

START DETECTED

12 SMBSUS SMBSUS

CLK

74HC74

U4A

CAPTURE_ENABLE

SMBCLK

SMBDATA_IN

MASK_ALERT2

J1–4

GND

4.7k

SMBSUS_DUT

U1E

74HC08 118

U3C

J1–8 10

START_DETECTED

MASK_START

CAPTURE_ENABLE

SMBCLK_IN

DRIVE_SCL_LOW

+5V

74HC05

SMBCLK

+5V

DECOUPLING CAP.

0.1µF

J1–13

J1–5 LOOPBACK

SMBCLK

U2B

U1A

U2C

74HC05

CLK

74HC74

U4B

U1F

74HC08 13 12

GRAB_SCL

CAPTURE_ENABLE

U3D

HOLDING_ CLOCK

J1–15

J1–18

J1–19

J1–9

4.7k

47k

+5V

SMBCLK

CAPTURE_ENABLE

J1–2 R5

4.7k

SMBCLK_OUT

74HC04

J1–12

74HC04

SMBCLK_IN

SMBDATA

U2D

U1B

74HC05

47k

+5V

SMBDATA

J1–3 R6

4.7k

SMBDATA_OUT

J1–11

74HC04

SMBDATA_IN

J2–1

INTERFACE TEST POINTS

HOLDING_CLOCK

J2–2 SMBCLK_OUT

J2–3 SMBDATA_OUT

J2–4 SMBSUS_OUT

J2–5 MASK_ALERT1

J2–6 MASK_ALERT2

J2–7 MASK_START

J2–8 CAPTURE_ENABLE

J2–9 INT

J2–10 SMBDATA_IN

J2–11 SMBCLK_IN

J2–12 GND

J1–20

J1–21

J1–22

J1–23

J1–24

J1–25

Figure 1. MAXSMBus Schematic

Evaluates: MAXSMBus

Two-Wire Interface Board

6 _______________________________________________________________________________________

P1–17

P1–15

P1–1

DUT +5V

DUT SDA

DUT SCL

P1–3

P1–5

P1–7

P1–2

P1–4

P1–6

P1–8

P1–10

P1–12

P1–14

P1–16

P1–18

P1–20

+9V

+5V

+10V

+5V

+9V

+5V

POS9

GND1

+9V

LM78L05ACM

3.3µF

25V

3.3µF

25V

3.3µF

25V

OUT

GND

N.C.

GND

N.C.

6.8V GND

SMBDATA

SMBCLK

SMBSUS

ALERT1

ALERT2

J1–1

J1–14

4.3V

-10V

POS5

SBDAT1

MAX367

SBCLK1

SBSUS1

ALERT1

ALERT2

GND0

GND

P1 2 x 10 RIGHT ANGLE HEADER

DUT SMBSUS

DUT SMBALERT P1–11

P1–9

DUT ALERT2

SPARE OUTPUT J1–1

SPARE OUTPUT J1–14

P1–13

P1–19

3.3µF

25V

3.3µF

25V

3.3µF

25V

+10V

+5V

-10V

GND

MAX865

C1+

C2+

C2-

V-

C1-

V+

GND

Figure 1. MAXSMBus Schematic (continued)

Evaluates: MAXSMBus

Two-Wire Interface Board

_______________________________________________________________________________________ 7

Figure 2. MAXSMBus Component Placement Guide Figure 3. MAXSMBus PC Board Layout—Component Side

1.0"

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.

8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Evaluates: MAXSMBus

Two-Wire Interface Board

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.

8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

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.

8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Figure 4. MAXSMBus PC Board Layout—Solder Side

1.0"