Datasheet

Section 13 8-Bit Timers (TMR)
R01UH0309EJ0500 Rev. 5.00 Page 825 of 1408
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
13.3.1 Timer Counter (TCNT)
TCNT is 8-bit up-counter. TCNT_0 and TCNT_1 comprise a single 16-bit register so they can be
accessed together by a word transfer instruction. Bits CKS2 to CKS0 in TCR are used to select a
clock. TCNT can be cleared by an external reset input or by a compare match signal A or B.
Which signal is to be used for clearing is selected by bits CCLR1 and CCLR0 in TCR. When
TCNT overflows from H'FF to H'00, OVF in TCSR is set to 1. TCNT is initialized to H'00.
13.3.2 Time Constant Register A (TCORA)
TCORA is 8-bit readable/writable register. TCORA_0 and TCORA_1 comprise a single 16-bit
register so they can be accessed together by a word transfer instruction. The value in TCORA is
continually compared with the value in TCNT. When a match is detected, the corresponding
CMFA flag in TCSR is set to 1. Note, however, that comparison is disabled during the T
2
state of a
TCORA write cycle. The timer output from the TMO pin can be freely controlled by this compare
match signal (compare match A) and the settings of bits OS1 and OS0 in TCSR. TCORA is
initialized to H'FF.
13.3.3 Time Constant Register B (TCORB)
TCORB is 8-bit readable/writable register. TCORB_0 and TCORB_1 comprise a single 16-bit
register so they can be accessed together by a word transfer instruction. TCORB is continually
compared with the value in TCNT. When a match is detected, the corresponding CMFB flag in
TCSR is set to 1. Note, however, that comparison is disabled during the T
2
state of a TCOBR write
cycle. The timer output from the TMO pin can be freely controlled by this compare match signal
(compare match B) and the settings of bits OS3 and OS2 in TCSR. TCORB is initialized to H'FF.