[Prev] [Next] [Contents] [Commodore] [New] [Search] [Home]

System Specification for C65Fred BowenMarch 1, 1991 Control Registers (CRA, CRB, CRC, CRD)

CRA (0XE):
BIT Bit Name Function
0 STARTA 1=START TIMER A, 0=STOP TIMER A. This bit is automatically reset when TIMER A underflow occurs during one-shot mode.
1 PRB6 ON 1=TIMER A output appears on PRB6, O=PRB6 normal port operation.
2 OUT-A MODE 1=TOGGLE output applied on port PRB6, 0=PULSE output applied on port PRB6.
3 RUN-A MODE 1=ONE-SHOT TIMER A operation, 0=CONTINUOUS TIMER A operation.
4 LOADA 1=FORCE LOAD on TIMER A (this is a STROBE input, there is no data storage, bit 4 will always read back a zero and writing a zero has no effect).
5 TMRA INMODE 1=TIMER A counts positive CNTA transitions, 0=TIMER A counts internal C1MHZ pulses.
6 SPA MODE 1=SERIAL A PORT output mode (CNTA sources shift clock), 0=SERIAL A PORT input mode (external shift clock on CNTA)
7 TODA IN 1=50 Hz operation. C7MHZ divided down by 101339 to generate TODA input of 10 Hz. 0=60 Hz operation. C7MHZ divided down by 102273 to generate TODA input of 10 Hz.
CRB (0XF):
BIT Bit Name Function
  (Bits 0-4 of the CRB register operate identically to bits 0-4 of the CRA register, except that functions now apply to TIMER B and bit 1 control the output of TIMER B on PRB7).
5,6 TIMERB Bits 5 and 6 select one of four input modes for TIMER B INMODE as follows:
0 0 TIMER B counts ClMHz pulses.
0 1 TIMER B counts positive CNTA transitions.
1 0 TIMER B counts TIMERA underflow pulses.
1 1 TIMER B counts TIMERA underflows while CNTA is high.
7 ALARM TODA 1=writing to TODA registers sets ALARM, 0=writing to TODA registers sets TODA clock.

[Prev] [Next] [Contents] [Commodore] [New] [Search] [Home]
This page has been created by Sami Rautiainen.
Read the small print. Last updated July 28, 2002.