MC68HC705P9CDW FREESCALE [Freescale Semiconductor, Inc], MC68HC705P9CDW Datasheet - Page 113

• Manufacturer Part Number: MC68HC705P9CDW
• Description: Microcontrollers
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

9.7.4 Alternate Timer Registers
MC68HC705P9 — Rev. 4.0
MOTOROLA
NOTE:
The read-only alternate timer registers (ATRH and ATRL) 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
does not affect the timer overflow flag (TOF). Writing to the alternate
timer registers has no effect.
Reading ATRH returns the current value of the high byte of the counter
and causes the low byte to be latched into a buffer.
To prevent interrupts between readings of ATRH and ATRL, set the
interrupt mask (I bit) in the condition code register before reading ATRH,
and clear the mask after reading ATRL.
$001A
Reset:
$001B
Reset:
Read:
Read:
Write:
Write:
Freescale Semiconductor, Inc.
Figure 9-14. Alternate Timer Registers (ATRH and ATRL)
For More Information On This Product,
Bit 15
Bit 7
Bit 7
Bit 7
Figure 9-15. Alternate Timer Register Reads
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READ ATRH
= Unimplemented
INTERNAL
DATA BUS
14
6
6
6
Timer
13
5
5
5
LATCH
Reset initializes ATRH to $FF
Reset initializes ATRL to $FC
ATRH ($001A)
12
4
4
4
11
3
3
3
ATRL ($001B)
BUFFER
10
2
2
2
1
9
1
1
Technical Data
I/O Registers
Bit 0
Bit 8
Bit 0
Bit 0
Timer
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