PIC16F917-I/PT - Microchip Technology

 2010 Microchip Technology Inc. DS80329B-page 1

TIMER1 MODULE

Clarifications/Corrections to the Data

Sheet:

In the Device data sheets listed below, the following

clarifications and corrections should be noted. Any

silicon issues related to the Timer1 Module will be

reported in a separate silicon errata. Please check the

Microchip web site for any existing issues.

Device Data

Sheet Device Data

Sheet

PIC12F609

DS41302

PIC16F716 DS41206 PIC18F2321 DS39689 PIC18F6585

DS30491

PIC12HV609 PIC16F737

DS30498

PIC18F4321 PIC18F6680

PIC12F615 PIC16F747 PIC18F2331

DS39616

PIC18F8585

PIC12HV615 PIC16F767 PIC18F2431 PIC18F8680

PIC12F617

PIC12F629 DS41190 PIC16F777 PIC18F4331 PIC18F24J10

DS39682

PIC12F675 PIC16F785 DS41249 PIC18F4431 PIC18F25J10

PIC12F635

DS41232

PIC16HV785 PIC18F2439

DS30485

PIC18F44J10

PIC16F636 PIC16F818 DS39598 PIC18F2539 PIC18F45J10

PIC16F639 PIC16F819 PIC18F4439 PIC18F63J11

DS39774

PIC12F683 DS41211 PIC16F870 DS30569 PIC18F4539 PIC18F64J11

PIC14000 DS40122 PIC16F871 PIC18F2455

DS39632

PIC18F65J11

PIC16C62A

DS30234

PIC16F872 DS30221 PIC18F2550 PIC18F83J11

PIC16C63 PIC16F873

DS30292

PIC18F4455 PIC18F84J11

PIC16C64A PIC16F874 PIC18F4550 PIC18F85J11

PIC16C65A PIC16F876 PIC18F2480

DS39637

PIC18F63J90

DS39770

PIC16C66 PIC16F877 PIC18F4480 PIC18F64J90

PIC16C67 PIC16F873A

DS39582

PIC18F4580 PIC18F65J90

PIC16C62B DS35008 PIC16F874A PIC18F2510

DS39636

PIC18F83J90

PIC16C72A PIC16F876A PIC18F2610 PIC18F84J90

PIC16C63A

DS30605

PIC16F877A PIC18F4510 PIC18F85J90

PIC16C65B PIC16F882

DS41291

PIC18F4610 PIC18F65J10

DS39663

PIC16C73B PIC16F883 PIC18F2520 DS39631 PIC18F65J15

PIC16C74B PIC16F884 PIC18F4520 PIC18F66J10

PIC16C72

DS30390

PIC16F886 PIC18F2585

DS39625

PIC18F66J15

PIC16C73A PIC16F887 PIC18F2680 PIC18F67J10

PIC16C74A PIC16F913

DS41250

PIC18F4585 PIC18F85J10

PIC16C76 PIC16F914 PIC18F4680 PIC18F85J15

PIC16C77 PIC16F916 PIC18F2620 DS39626 PIC18F86J10

PIC16C745 DS41124 PIC16F917 PIC18F4620 PIC18F85J15

PIC16C765 PIC16F946 PIC18F87J10

Timer1 Module Data Sheet Errata

TIMER1 MODULE

DS80329B-page 2  2010 Microchip Technology Inc.

PIC16C773 DS30275 PIC17C42A

DS30412

PIC18F4685 DS39761 PIC18F65J50

DS39775

PIC16C774 PIC17C43 PIC18F6390

DS39629

PIC18F66J50

PIC16C923 DS30444 PIC17C44 PIC18F6490 PIC18F66J55

PIC16C924 PIC17C752

DS30289

PIC18F8390 PIC18F67J50

PIC16C925 DS39544 PIC17C756A PIC18F8490 PIC18F85J50

PIC16C926 PIC17C762 PIC18F6520

DS39609

PIC18F85J55

PIC16F72 DS39597 PIC17C766 PIC18F6620 PIC18F87J50

PIC16F73

DS30325

PIC18C242

DS39026

PIC18F6720 PIC18F66J11

DS39778

PIC16F74 PIC18C252 PIC18F8520 PIC18F66J16

PIC16F76 PIC18C442 PIC18F8620 PIC18F67J11

PIC16F77 PIC18C452 PIC18F8720 PIC18F86J11

PIC16F87 DS30487 PIC18C601 DS39541 PIC18F6525

DS39612

PIC18F86J16

PIC16F88 PIC18C801 PIC18F6621 PIC18F87J11

PIC16F610

DS41288

PIC18C658 DS30475 PIC18F8525 PIC18F66J60

DS39762

PIC16HV610 PIC18C858 PIC18F8621 PIC18F66J65

PIC16F616 PIC18F242

DS39564

PIC18F6527

DS39646

PIC18F67J60

PIC16HV616 PIC18F252 PIC18F6622 PIC18F86J60

PIC16F627A

DS40044

PIC18F442 PIC18F6627 PIC18F86J65

PIC16F628A PIC18F452 PIC18F6722 PIC18F87J60

PIC16F648A PIC18F248

DS41159

PIC18F8527 PIC18F96J60

PIC16F630 DS40039 PIC18F258 PIC18F8622 PIC18F96J65

PICF676 PIC18F458 PIC18F8627 PIC18F97J60

PIC16F631

DS41262

PIC18F1220 DS39605 PIC18F8722

PIC16F677 PIC18F1320

PIC16F685 PIC18F1230 DS39758

PIC16F687 PIC18F1330

PIC16F689 PIC18F2220

DS39599

PIC16F690 PIC18F2330

PIC16F684 DS41202 PIC18F4220

PIC16F688 DS41203 PIC18F4320

Device Data

Sheet Device Data

Sheet

 2010 Microchip Technology Inc. DS80329B-page 3

TIMER1 MODULE

1. Asynchronous Counter

When Timer1 is started or updated, the timer

needs to see a falling edge from the external clock

source before a rising edge can increment the

counter. If writes to TMR1H and TMR1L are not

completed while the external clock pulse is still

high, Timer1 will miss counting the first clock pulse

after the update.

When using an external crystal, the pulse width

from rising to falling edge is temperature depen-

dent and may decrease with temperature. As a

result, the timer may require an additional oscilla-

tion to overflow.

Code examples are given for the affected devices:

• PIC12/14/16/17 devices – Example 1 and

Example 2

• PIC18 devices – Example 3

Both examples include code to wait for Timer1 to

increment twice between the RTCisr and Update

labels.

In PIC18 devices, it is not possible to reliably

update Timer1 in a low-priority interrupt. A high-

priority interrupt could occur at any time and

unexpectedly delay the TMR1 update.

PIC18 devices also include Timer3 which is

functionally identical to Timer1.

Work around

Switching Timer1 to the main system oscillator

after reloading, the timer ensures the timer will see

a falling edge before switching back to the external

clock source.

Due to the time from Timer1 overflow to the reload

being application specific, wait for the timer to

increment before beginning the reload sequence.

This ensures the timer does not miss a rising edge

during reload. The timing of the clock source

changing is critical and is detailed in Example 1

and Example 2.

EXAMPLE 1: PIC12/14/16/17 CODE EXAMPLE FOR 1 SECOND OVERFLOW PERIOD WITH 32.786

kHZ OSCILLATOR

BTFSC TMR1L,0

GOTO $-1

BTFSS TMR1L,0

GOTO $-1 ;Timer has just incremented, 31 μs before next rising edge to

;complete reload

Update:

BCF T1CON,TMR1CS ;Select system clock for Timer1

BSF TMR1H,7 ;Timer1 high byte 0x80

BCF T1CON,TMR1ON ;Timer1 off

BSF T1CON,TMR1C ;Select external crystal

BSF T1CON,TMR1ON ;Timer1 on

Critical Timing of code sequence for instructions following last write to TMR1L or TMR1H.

TIMER1 MODULE

DS80329B-page 4  2010 Microchip Technology Inc.

EXAMPLE 2: PIC12/14/16/17 CODE EXAMPLE FOR OVERFLOW PERIODS OTHER THAN 1

SECOND OR USING AN OSCILLATOR OTHER THAN 32.768 kHZ

EXAMPLE 3: PIC18 HIGH-PRIORITY INTERRUPT SERVICE ROUTINE

BTFSC TMR1L, 0

GOTO $-1

BTFSS TMR1L, 0

GOTO $-1 ;Timer has just incremented, 31μs before next rising

edge to complete reload.

BCF T1CON, TMR1CS ;Select system clock for Timer1.

MOVF TMR1, W ;Sample low byte of Timer1 before increments.

ADDWF TMR1_Reload_lo, F ;Add reload value for low byte

BTFSC STATUS, C ;if this generates a carry then

INCF TMR1_Reload_hi, F ;modify the reload value for the high byte.

MOVF TMR1_Reload_hi, W ;Reload Timer1 high byte.

MOVWF TMR1H

MOVF TMR1_Reload_lo, W ;Reload Timer1 low byte.

MOVW TMR1L

BCF T1CON, TMR1ON ;Timer1 off.

BSF T1CON, TMR1CS ;Select external crystal.

BSF T1CON, TMR1ON ;Timer1 on.

Critical Timing of code sequence for instructions.

HIntVector code 0x0008 ; (3-4Tcy), fixed interrupt latency

goto HighISR ; (3Tcy) jump to high priority ISR code

code ; unprotected code space

HighISR:

btfss PIR1,TMR1IF ; (1Tcy) TMR1 overflow?

goto NextISR ; (2Tcy) No, check another interrupt source

; Insert the next 4 lines of code when TMR1 can not

; be reliably updated before clock pulse goes low

RTCisr:

btfsc TMR1L,0 ; wait for TMR1L<0> to become clear

bra $-2 ; may already be clear (loops for 0 to 30.5us)

btfss TMR1L,0 ; wait for TMR1L<0> to become set

bra $-2 ; (loops for 30.5us)

; If TMR1 update can be completed before clock pulse

; goes low, start update here

Update:

bsf TMR1H,7 ; reload for next 1 second overflow

bcf PIR1,TMR1IF ; clear flag

incf Seconds,F ; record second

retfie FAST

NextISR: ; Another interrupt source...

.... ; code for other interrupts, if needed

retfieFAST

 2010 Microchip Technology Inc. DS80329B-page 5

TIMER1 MODULE

REVISION HISTORY

Rev A Document (7/2007)

Initial release of this errata.

Rev B Document (03/2010)

Added PIC12F617 device to the Clarifications/

Corrections to the Data Sheet section.

TIMER1 MODULE

DS80329B-page 6  2010 Microchip Technology Inc.

NOTES:

 2010 Microchip Technology Inc. DS80329B-page 7

Information contained in this publication regarding device

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and may be superseded by updates. It is your responsibility to

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Printed on recycled paper.

ISBN: 978-1-60932-048-5

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DS80329B-page 8  2010 Microchip Technology Inc.

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