PIC17C752 MICROCHIP [Microchip Technology], PIC17C752 Datasheet - Page 104

• Manufacturer Part Number: PIC17C752
• Description: High-Performance 8-Bit CMOS EPROM Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

13.2.4
When TMR3CS is set, the 16-bit TMR3 increments on
the falling edge of clock input TCLK3. The input on the
RB5/TCLK3 pin is sampled and synchronized by the
internal phase clocks twice every instruction cycle. This
causes a delay from the time a falling edge appears on
TCLK3 to the time TMR3 is actually incremented. For
the external clock input timing requirements, see the
Electrical Specification section. Figure 13-10 shows
the timing diagram when operating from an external
clock.
EXAMPLE 13-2: WRITING TO TMR3
EXAMPLE 13-3: READING FROM TMR3
FIGURE 13-10: TIMER1, TIMER2, AND TIMER3 OPERATION (IN COUNTER MODE)
DS30264A-page 104
PR1, PR2, or PR3H:PR3L
BSF
MOVFP
MOVFP
BCF
MOVPF
MOVPF
MOVFP
CPFSLT
RETURN
MOVPF
MOVPF
RETURN
TMR1, TMR2, or TMR3
EXTERNAL CLOCK INPUT FOR TIMER3
CPUSTA, GLINTD
RAM_L,
RAM_H,
CPUSTA, GLINTD
TMR3L, TMPLO
TMR3H, TMPHI
TMPLO, WREG
TMR3L, WREG
TMR3L, TMPLO
TMR3H, TMPHI
Instruction
executed
WR_TMR
or TCLK3
RD_TMR
TCLK12
TMRxIF
TMR3L
TMR3H
Note 1: TCLK12 is sampled in Q2 and Q4.
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
'A9h'
34h
3: The latency from TCLK12
; read low TMR3
; read high TMR3
; tmplo
; TMR3L < wreg?
; no then return
; read low TMR3
; read high TMR3
; return
; Disable interrupts
;
;
; Done, enable interrupts
indicates a sampling point.
Write to TMRx
MOVWF
TMRx
35h
Preliminary
wreg
Read TMRx
MOVFP
TMRx,W
A8h
13.2.5
Since Timer3 is a 16-bit timer and only 8-bits at a time
can be read or written, care should be taken when
reading or writing while the timer is running. The best
method is to stop the timer, perform any read or write
operation, and then restart Timer3 (using the TMR3ON
bit). However, if it is necessary to keep Timer3 free-run-
ning, care must be taken. For writing to the 16-bit
TMR3, Example 13-2 may be used. For reading the
16-bit TMR3, Example 13-3 may be used. Interrupts
must be disabled during this routine.
to timer increment is between 2Tosc and 6Tosc.
Read TMRx
MOVFP
TMRx,W
READING/WRITING TIMER3
A9h
1997 Microchip Technology Inc.
'A9h'
00h