2.6 8254 Timer/Counter
The 8254 Programmable timer/counter has 4 registers from Base+0 through Base+3. For
detailed programming information about the 8254 , please refer to Intel‘s “Microsystem
Components Handbook”.The block diagram is shown below.
Cin : clock input
Cout : clock output
INTCLK : internal clock
CN3 : connector CN3
Cin
Gate
Cout
Counter 0
Cin
Gate Cout
Counter 1
Cin
Gate Cout
Counter 2
4M
2M
INTCLK
VCC
10K
CN3.37
PACER CLK
JP6
2M
CN3.35
CN3.16
CN3.33
VCC
10K
CN3.34
The counter0, counter1 and counter2 are all 16 bit counters. Counter 1 and counter 2 are
cascaded as a 32 bit timer. This 32 bit timer is used as a
pacer timer
.
The software driver,
A-822_Delay(), uses counter 0 to implement a machine independent timer for settling
time delay (sec. 2.4.6 and sec. 2.4.7).
If A-822_Delay() is not used, counter0 can be used as
a general purpose timer/counter.
NOTE : When using A-822_Delay() to implement a machine
independent timer, the JP6 jumper must be set to internal 2M
clock.
OME-A-822PGL/PGH Hardware Manual ----
26
