mc68hc05p9a Freescale Semiconductor, Inc, mc68hc05p9a Datasheet - Page 99

• Manufacturer Part Number: mc68hc05p9a
• Description: Hcmos Microcontroller Unit
• Manufacturer: Freescale Semiconductor, Inc

Alternate Timer
Registers
19-tim1ic1oc_a
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.
For More Information On This Product,
Figure 55. Alternate Timer Registers (ATRH and ATRL)
Bit 15
Bit 7
Bit 7
Bit 7
Go to: www.freescale.com
Figure 56. Alternate Timer Register Reads
= Unimplemented
READ ATRH
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
I/O Registers
Bit 0
Bit 0
Bit 8
Bit 0
Timer
99