HD64F3694HV Datasheet, PDF (165/452 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

Section 10 Timer A
10.4 Operation
10.4.1 Interval Timer Operation
When bit TMA3 in TMA is cleared to 0, timer A functions as an 8-bit interval timer.
Upon reset, TCA is cleared to H'00 and bit TMA3 is cleared to 0, so up-counting of timer A
resume immediately as an interval timer. The clock input to timer A is selected by bits TMA2 to
TMA0 in TMA; any of eight internal clock signals output by prescaler S can be selected.
After the count value in TCA reaches H'FF, the next clock signal input causes timer A to
overflow, setting bit IRRTA to 1 in interrupt Flag Register 1 (IRR1). If IENTA = 1 in interrupt
enable register 1 (IENR1), a CPU interrupt is requested. At overflow, TCA returns to H'00 and
starts counting up again. In this mode timer A functions as an interval timer that generates an
overflow output at intervals of 256 input clock pulses.
10.4.2 Clock Time Base Operation
When bit TMA3 in TMA is set to 1, timer A functions as a clock-timer base by counting clock
signals output by prescaler W. When a clock signal is input after the TCA counter value has
become H'FF, timer A overflows and IRRTA in IRR1 is set to 1. At that time, an interrupt request
is generated to the CPU if IENTA in the interrupt enable register 1 (IENR1) is 1. The overflow
period of timer A is set by bits TMA1 and TMA0 in TMA. A choice of four periods is available.
In clock time base operation (TMA3 = 1), setting bit TMA2 to 1 clears both TCA and prescaler W
to H'00.
10.4.3 Clock Output
Setting bit TMOW in port mode register 1 (PMR1) to 1 causes a clock signal to be output at pin
TMOW. Eight different clock output signals can be selected by means of bits TMA7 to TMA5 in
TMA. The system clock divided by 32, 16, 8, or 4 can be output in active mode and sleep mode. A
32.768 kHz signal divided by 32, 16, 8, or 4 can be output in active mode, sleep mode, and
subactive mode.
10.5 Usage Note
When the clock time base function is selected as the internal clock of TCA in active mode or sleep
mode, the internal clock is not synchronous with the system clock, so it is synchronized by a
synchronizing circuit. This may result in a maximum error of 1/φ (s) in the count cycle.
Rev.5.00 Nov. 02, 2005 Page 135 of 418
REJ09B0028-0500