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Rev. 1.00, 05/04, page 191 of 544
10.3.1 Timer Counter (TCNT)
Each TCNT is an 8-bit readable/writable up-counter. TCNT_0 and TCNT_1 comprise a single 16-
bit register, so they can be accessed together by word access. The clock source is selected by the
CKS2 to CKS0 bits in TCR. TCNT can be cleared by an external reset input signal, compare-
match A signal or compare-match B signal. The method of clearing can be selected by the CCLR1
and CCLR0 bits in TCR. When TCNT overflows (changes from H'FF to H'00), the OVF bit in
TCSR is set to 1. TCNT is initialized to H'00.
TCNT_Y can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS is 1.
TCNT_X can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS is 0.
10.3.2 Time Constant Register A (TCORA)
TCORA is an 8-bit readable/writable register. TCORA_0 and TCORA_1 comprise a single 16-bit
register, so they can be accessed together by word access. TCORA is continually compared with
the value in TCNT. When a match is detected, the corresponding compare-match flag A (CMFA)
in TCSR is set to 1. Note however that comparison is disabled during the T2 state of a TCORA
write cycle. The timer output from the TMO pin can be freely controlled by these compare-match
A signals and the settings of output select bits OS1 and OS0 in TCSR. TCORA is initialized to
H'FF.
TCORA_Y can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS is
1. TCORA_X can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS
is 0.
10.3.3 Time Constant Register B (TCORB)
TCORB is an 8-bit readable/writable register. TCORB_0 and TCORB_1 comprise a single 16-bit
register, so they can be accessed together by word access. TCORB is continually compared with
the value in TCNT. When a match is detected, the corresponding compare-match flag B (CMFB)
in TCSR is set to 1. Note however that comparison is disabled during the T2 state of a TCORB
write cycle. The timer output from the TMO pin can be freely controlled by these compare-match
B signals and the settings of output select bits OS3 and OS2 in TCSR. TCORB is initialized to
H'FF.
TCORB_Y can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS is
1. TCORB_X can be accessed when the HIE bit in SYSCR is 0 and the TMRX/Y bit in TCONRS
is 0.