7.1.4 Register Configuration
Table 7-2 lists the registers of the 8-bit timer module. Each channel has an independent set of
registers.
Table 7-2. 8-Bit Timer Registers
Note: * Software can write a “0” to clear bits 7 to 5, but cannot write a “1” in these bits.
7.2 Register Descriptions
7.2.1 Timer Counter (TCNT)—H'FFCC (TMR0), H'FFD4 (TMR1)
Bit
7
6
5
4
3
2
1
0
Initial value
0
0
0
0
0
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
Each timer counter (TCNT) is an 8-bit up-counter that increments on a pulse generated from an
internal or external clock source selected by clock select bits 2 to 0 (CKS2 to CKS0) of the timer
control register (TCR). The CPU can always read or write the timer counter.
The timer counter can be cleared by an external reset input or by an internal compare-match signal
generated at a compare-match event. Clock clear bits 1 and 0 (CCLR1 and CCLR0) of the timer
control register select the method of clearing.
When a timer counter overflows from H'FF to H'00, the overflow flag (OVF) in the timer
control/status register (TCSR) is set to “1.”
Address
Name
Abbreviation
R/W
Initial value
TMR0
TMR1
Timer control register
TCR
R/W
H'00
H'FFC8
H'FFD0
Timer control/status register
TCSR
R/(W)*
H'10
H'FFC9
H'FFD1
Timer constant register A
TCORA
R/W
H'FF
H'FFCA
H'FFD2
Timer constant register B
TCORB
R/W
H'FF
H'FFCB
H'FFD3
Timer counter
TCNT
R/W
H'00
H'FFCC
H'FFD4
Serial/timer control register
STCR
R/W
H'F8
H'FFC3
H'FFC3
145
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