Datasheet

Timer Interface Module A (TIMA)
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
318 Freescale Semiconductor
NOTE
Do not set the TSTOP bit before entering wait mode if the TIMA is required
to exit wait mode. Also, when the TSTOP bit is set and input capture mode
is enabled, input captures are inhibited until TSTOP is cleared.
When using the TSTOP to stop the timer counter, see if any timer flags are
set. If a timer flag is set, it must be cleared by clearing the TSTOP, then
clearing the flag, then setting the TSTOP again.
TRST — TIMA Reset Bit
Setting this write-only bit resets the TIMA counter and the TIMA prescaler. Setting TRST has no effect
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMA
counter is reset and always reads as logic 0. Reset clears the TRST bit.
1 = Prescaler and TIMA counter cleared
0 = No effect
NOTE
Setting the TSTOP and TRST bits simultaneously stops the TIMA counter
at a value of $0000.
PS[2:0] — Prescaler Select Bits
These read/write bits select either the PTD6/ATD14/TACLK pin or one of the seven prescaler outputs
as the input to the TIMA counter as Table 25-1 shows. Reset clears the PS[2:0] bits.
25.8.2 TIMA Counter Registers
The two read-only TIMA counter registers contain the high and low bytes of the value in the TIMA counter.
Reading the high byte (TACNTH) latches the contents of the low byte (TACNTL) into a buffer. Subsequent
reads of TACNTH do not affect the latched TACNTL value until TACNTL is read. Reset clears the TIMA
counter registers. Setting the TIMA reset bit (TRST) also clears the TIMA counter registers.
NOTE
If TACNTH is read during a break interrupt, be sure to unlatch TACNTL by
reading TACNTL before exiting the break interrupt. Otherwise, TACNTL
retains the value latched during the break.
Table 25-1. Prescaler Selection
PS[2:0] TIMA Clock Source
000 Internal Bus Clock ÷1
001 Internal Bus Clock ÷ 2
010 Internal Bus Clock ÷ 4
011 Internal Bus Clock ÷ 8
100 Internal Bus Clock ÷ 16
101 Internal Bus Clock ÷ 32
110 Internal Bus Clock ÷ 64
111 PTD6/ATD14/TACLK