9.2
Register Descriptions
9.2.1
Timer Counter (TCNT)
Bit
7
6
5
4
3
2
1
0
Initial value
Read/Write
0
0
0
0
0
0
0
0
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.
The timer counters are initialized to H'00 by a reset and in the standby modes.
9.2.2
Time Constant Registers A and B (TCORA and TCORB)
Bit
7
6
5
4
3
2
1
0
Initial value
Read/Write
1
1
1
1
1
1
1
1
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
TCORA and TCORB are 8-bit readable/writable registers. The timer count is continually
compared with the constants written in these registers (except during the T3 state of a write cycle
to TCORA or TCORB). When a match is detected, the corresponding compare-match flag (CMFA
or CMFB) is set in the timer control/status register (TCSR).
The timer output signal is controlled by these compare-match signals as specified by output select
bits 3 to 0 (OS3 to OS0) in the timer control/status register (TCSR).
TCORA and TCORB are initialized to H'FF by a reset and in the standby modes.
192
HITACHI [ HITACHI SEMICONDUCTOR ]
