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); |
Prometheus CPU User Manual V1.44 | Page 61 |
