Timer Operation - Hitachi H8/3937 Series Hardware Manual

4. Subclock Output Select Register (CWOSR)
7
Bit:
—
Initial value: 1
Read/Write:
—
CWOSR is an 8-bit read/write register that selects the clock to be output from the TMOW pin.
CWOSR is initialized to H'FE by a reset.
Bits 7 to 1: Reserved bits
Bits 7 to 1 are reserved; they are always read as 1 and cannot be modified.
Bit 0: TMOW pin clock select (CWOS)
Bit 0 selects the clock to be output from the TMOW pin.
Bit 0
CWOS Description
0 Clock output from timer A is output (see TMA)
1 ø is output
W
9.2.3

Timer Operation

1. Interval timer operation
When bit TMA3 in timer mode register A (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 and interval
timing resume immediately. 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 request 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.
Note: * For details on interrupts, see 3.3, Interrupts.
186
6 5
— — —
1 1
— — —
4 3 2
— —
1 1 1
— —
1 0
CWOS
—
1 0
R/W
—
(initial value)