MC68HC05C9A Datasheet, PDF (49/124 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer I/O Registers
8.3.3 Timer Registers
The timer registers (TRH and TRL), shown in Figure 8-4, contain the current high and low bytes of the
16-bit counter. Reading TRH before reading TRL causes TRL to be latched until TRL is read. Reading
TRL after reading the timer status register clears the timer overflow flag (TOF). Writing to the timer
registers has no effect.
Address: $0018 — TRH
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
Address: $0019 — TRL
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
0
0
= Unimplemented
Figure 8-4. Timer Registers (TRH and TRL)
8.3.4 Alternate Timer Registers
The alternate timer registers (ATRH and ATRL), shown in Figure 8-5, contain the current high and low
bytes of the 16-bit counter. Reading ATRH before reading ATRL causes ATRL to be latched until ATRL
is read. Reading ATRL has no effect on the timer overflow flag (TOF). Writing to the alternate timer
registers has no effect.
Address: $001A — ATRH
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
Address: $001B — ATRL
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
0
0
= Unimplemented
Figure 8-5. Alternate Timer Registers (ATRH and ATRL)
NOTE
To prevent interrupts from occurring between readings of ATRH and ATRL,
set the interrupt flag in the condition code register before reading ATRH,
and clear the flag after reading ATRL.
MC68HC05C9A Advance Information Data Sheet, Rev. 5.1
Freescale Semiconductor
49