302
11.2.2
Timer Control/Status Register (TCSR)
TCSR is an 8-bit readable and writable register. Its functions include selecting the timer mode and
clock source.
Bit
Initial value
Read/Write
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
Overflow flag
Status flag indicating overflow
Clock select
These bits select the
TCNT clock source
Timer mode select
Selects the mode
Timer enable
Selects whether TCNT runs or halts
Reserved bits
*
Notes: The method for writing to TCSR is different from that for general registers to prevent
inadvertent overwriting. For details see section 11.2.4, Notes on Register Access.
*
Only 0 can be written, to clear the flag.
Bits 7 to 5 are initialized to 0 by a reset and in standby mode. Bits 2 to 0 are initialized to 0 by a
reset. In software standby mode bits 2 to 0 are not initialized, but retain their previous values.
Bit 7—Overflow Flag (OVF): This status flag indicates that the timer counter has overflowed
from H'FF to H'00.
Bit 7
OVF
Description
0
[Clearing condition]
Cleared by reading OVF when OVF = 1, then writing 0 in OVF
(Initial value)
1
[Setting condition]
Set when TCNT changes from H'FF to H'00
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