KS57C2308/P2308/C2316/P2316 TIMERS and TIMER/COUNTERS
11-5
BASIC TIMER COUNTER (BCNT)
BCNT is an 8-bit counter for the basic timer. It can be addressed by 8-bit read instructions.
RESET leaves the BCNT counter value undetermined. BCNT is automatically cleared to logic zero whenever the
BMOD register control bit (BMOD.3) is set to "1" to restart the basic timer. It is incremented each time a clock
pulse of the frequency determined by the current BMOD bit settings is detected.
When BCNT has incremented to hexadecimal “FFH” (255 clock pulses), it is cleared to “00H” and an overflow is
generated. The overflow causes the interrupt request flag, IRQB, to be set to logic one. When the interrupt
request is generated, BCNT immediately resumes counting with incoming clock signal.
NOTE
Always execute a BCNT read operation twice to eliminate the possibility of reading unstable data while
the counter is incrementing. If, after two consecutive reads, the BCNT values match, you can select the
latter value as valid data. Until the results of the consecutive reads match, however, the read operation
must be repeated until the validation condition is met.
BASIC TIMER OPERATION SEQUENCE
The basic timer's sequence of operations may be summarized as follows:
1. Set counter buffer bit (BMOD.3) to logic one to restart the basic timer.
2. BCNT is then incremented by one per each clock pulse corresponding to BMOD selection.
3. BCNT overflows if BCNT = 255 (BCNT = FFH).
4. When an overflow occurs, the IRQB flag is set by hardware to logic one.
5. The interrupt request is generated.
6. BCNT is then cleared by hardware to logic zero.
7. Basic timer resumes counting clock pulses.