Prometheus CPU User Manual V1.44
Page 61
Reading a counter
a. Latch the counter:
Counter 0
Counter 1
outp(base+15,0x40); outp(base+15,0xC0);
b. Read the data:
The value is returned in 3 bytes, low, middle, and high (2 bytes for counter 1)
Counter 0
Counter 1
low=inp(base+12); low=inp(base+12);
middle=inp(base+13); high=inp(base+13);
high=inp(base+14);
c. Assemble the bytes into the complete counter value:
Counter 0
Counter 1
val = high * 2^16 + middle * 2^8 + low;
val = high * 2^8 + low;
Enabling the counter gate
Counter 0
Counter 1
outp(base+15,0x10); outp(base+15,0x90);
The counter will run only when the gate input is high.
Disabling the counter gate
Counter 0
Counter 1
outp(base+15,0x20); outp(base+15,0xA0);
The counter will run continuously.
Clearing a counter
Clearing a counter is done when you want to restart an operation. Normally you only clear a
counter after you have stopped (disabled) and read the counter. If you clear a counter while it is
still enabled, it will continue to count incoming pulses, so its value may not stay at zero.
a. Stop (disable) the counter:
Counter 0
Counter 1
outp(base+15,0x08); outp(base+15,0x88);
b. Read the data (optional). See “Reading a counter” above.
c. Clear the counter:
Counter 0
Counter 1
outp(base+15,0x01); outp(base+15,0x81);
