MC68HC08AZ32A Datasheet, PDF (248/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Timer Interface Module A (TIMA)
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 17-1 shows. Reset clears the PS[2:0] bits.
Table 17-1. Prescaler Selection
PS[2:0]
000
001
010
011
100
101
110
111
TIMA Clock Source
Internal Bus Clock ÷1
Internal Bus Clock ÷ 2
Internal Bus Clock ÷ 4
Internal Bus Clock ÷ 8
Internal Bus Clock ÷ 16
Internal Bus Clock ÷ 32
Internal Bus Clock ÷ 64
PTD6/ATD14/TACLK
17.8.2 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.
Register Name and Address
TACNTH — $0022
Bit 7
6
5
4
3
2
1
Bit 0
Read: BIT 15 BIT 14 BIT 13 BIT 12 BIT 11 BIT 10
BIT 9
BIT 8
Write:
Reset: 0
0
0
0
0
0
0
0
Register Name and Address
TACNTL — $0023
Bit 7
6
5
4
3
2
1
Bit 0
Read: BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
Write:
Reset: 0
0
0
0
0
0
0
0
= Unimplemented
Figure 17-6. TIMA Counter Registers (TACNTH and TACNTL)
17.8.3 TIMA Counter Modulo Registers
The read/write TIMA modulo registers contain the modulo value for the TIMA counter. When the TIMA
counter reaches the modulo value, the overflow flag (TOF) becomes set and the TIMA counter resumes
counting from $0000 at the next timer clock. Writing to the high byte (TAMODH) inhibits the TOF bit and
overflow interrupts until the low byte (TAMODL) is written. Reset sets the TIMA counter modulo registers.
MC68HC08AZ32A Data Sheet, Rev. 2
248
Freescale Semiconductor