HD6473887 Datasheet, PDF (205/523 Pages) Renesas Technology Corp – Hitachi Single-Chip Microcomputer

2. Real-time clock time base operation
When bit TMA3 in TMA is set to 1, timer A functions as a real-time clock time base by counting
clock signals output by prescaler W. The overflow period of timer A is set by bits TMA1 and
TMA0 in TMA. A choice of four periods is available. In time base operation (TMA3 = 1), setting
bit TMA2 to 1 clears both TCA and prescaler W to their initial values of H'00.
3. Clock output
Setting bit TMOW in port mode register 1 (PMR1) to 1 causes a clock signal to be output at pin
TMOW. Nine different clock output signals can be selected by means of bits TMA7 to TMA5 in
TMA and bit CWOS in CWOSR. The system clock divided by 32, 16, 8, or 4 can be output in
active mode and sleep mode. A 32.768 kHz or 38.4 kHz signal divided by 32, 16, 8, or 4 can be
output in active mode, sleep mode, watch mode, subactive mode, and subsleep mode. The 32.768
kHz or 38.4 kHz clock is output in all modes except the reset state.
9.2.4 Timer A Operation States
Table 9-4 summarizes the timer A operation states.
Table 9-4 Timer A Operation States
Operation Mode
Reset Active Sleep
Watch
Sub-
active
Sub-
sleep
Module
Standby Standby
TCA Interval
Reset Functions Functions Halted Halted Halted Halted Halted
Clock time base Reset Functions Functions Functions Functions Functions Halted Halted
TMA
Reset Functions Retained Retained Functions Retained Retained Retained
Note:
When the real-time 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/ø (s) in
the count cycle.
188