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11.2
Register Descriptions
11.2.1
Timer Counter (TCNT)
7
0
R/W
6
0
R/W
5
0
R/W
4
0
R/W
3
0
R/W
0
R/W
2
0
R/W
1
0
R/W
Bit
:
Initial value :
R/W
:
TCNT is an 8-bit readable/writable* up-counter.
When the TME bit is set to 1 in TCSR, TCNT starts counting pulses generated from the internal
clock source selected by bits CKS2 to CKS0 in TCSR. When the count overflows (changes from
H'FF to H'00), the OVF flag in TCSR is set to 1.
TCNT is initialized to H'00 by a reset, in hardware standby mode, or when the TME bit is cleared
to 0. It is not initialized in software standby mode.
Note: * TCNT is write-protected by a password to prevent accidental overwriting. For details see
section 11.2.4, Notes on Register Access.
11.2.2
Timer Control/Status Register (TCSR)
7
OVF
0
R/(W)*
6
WT/IT
0
R/W
5
TME
0
R/W
4
—
1
—
3
—
1
—
0
CKS0
0
R/W
2
CKS2
0
R/W
1
CKS1
0
R/W
Bit
:
Initial value :
R/W
:
Note: * Only 0 can be written, to clear the flag.
TCSR is an 8-bit readable/writable* register. Its functions include selecting the clock source to be
input to TCNT, and the timer mode.
TCSR0 is initialized to H'18 by a reset and in hardware standby mode. It is not initialized in
software standby mode.
Note: * TCSR is write-protected by a password to prevent accidental overwriting. For details see
section 11.2.4, Notes on Register Access.
Bit 7—Overflow Flag (OVF): A status flag that indicates that TCNT has overflowed from H'FF
to H'00.