MC68HC908AT32 Datasheet, PDF (300/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer Interface (TIM-6)
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.
Register Name and Address: TCNTH — $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: R
R
R
R
R
R
R
R
Reset: 0
0
0
0
0
0
0
0
Register Name and Address: TCNTL — $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: R
R
R
R
R
R
R
R
Reset: 0
0
0
0
0
0
0
0
R
= Reserved
Figure 25-5. TIMA Counter Registers (TCNTH and TCNTL)
25.8.3 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 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.
Register Name and Address: TAMODH — $0024
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: 1
1
1
1
1
1
1
1
Register Name and Address: TAMODL — $0025
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: 1
1
1
1
1
1
1
1
Figure 25-6. TIMA Counter Modulo Registers (TAMODH and TAMODL)
NOTE
Reset the TIMA counter before writing to the TIMA counter modulo registers.
MC68HC908AT32 Data Sheet, Rev. 3.1
300
Freescale Semiconductor