166
Bits 3 to 0—Internal Clock Select (TMA3 to TMA0): Bits 3 to 0 select the clock input to TCA.
The selection is made as follows.
Description
Bit 3:
TMA3
Bit 2:
TMA2
Bit 1:
TMA1
Bit 0:
TMA0
Prescaler and Divider Ratio
or Overflow Period
Function
0
0
0
0
PSS, ø/8192
(Initial value)
Interval timer
1
PSS, ø/4096
1
0
PSS, ø/2048
1
PSS, ø/512
1
0
0
PSS, ø/256
1
PSS, ø/128
1
0
PSS, ø/32
1
PSS, ø/8
1
0
0
0
PSW, 1 s
Clock time base
1
PSW, 0.5 s
1
0
PSW, 0.25 s
1
PSW, 0.03125 s
1
0
0
PSW and TCA are reset
1
1
0
1
10.2.2
Timer Counter A (TCA)
Bit
7
6
5
4
3
2
1
0
TCA7
TCA6
TCA5
TCA4
TCA3
TCA2
TCA1
TCA0
Initial value
0
0
0
0
0
0
0
0
Read/Write
R
R
R
R
R
R
R
R
TCA is an 8-bit read-only up-counter, which is incremented by internal clock input. The clock
source for input to this counter is selected by bits TMA3 to TMA0 in timer mode register A
(TMA). TCA values can be read by the CPU in active mode, but cannot be read in subactive
mode. When TCA overflows, the IRRTA bit in interrupt request register 1 (IRR1) is set to 1.
TCA is cleared by setting bits TMA3 and TMA2 of TMA to 11.
Upon reset, TCA is initialized to H'00.
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