User`s guide

Operation Theorem  45
4.5 Timer/Counter Operation
The ACL-8316/12 has an 8254 programmable interval timer/counter on board.
It offers 3 independent 16-bit programmable down counters; counter 1 and
counter 2 are cascaded together for A/D timer pacer trigger of A/D
conversion, counter 0 is free for your applications. Figure 4.5 shows the 8254
timer/counter connection.
Counter 0
Counter 1
Counter 2
CLK0
GATE0 OUT0
CLK1
GATE1
CLK2
GATE2
OUT1
OUT2
2MHz
Oscillator
Vcc
Timer Pace
r
CN3 Pin-34
CN3 Pin-37
CN3 Pin-33
CN3 Pin-16
INT
EXT
8254 Timer/Counte
r
Figure 4.5 Block Diagram of 8254 Timer/Counter
The clock source of counter 0 can be internal or external, while it’s gate can
be controlled externally and the output is send to the connector CN3. As to
counter 1 and counter 2, the gates are internally pulled high and still can be
controlled externally. All clock sources and outputs of counter 1 and counter 2
are internally fixed and can’t be accessed via any connector. All the
timer/counter signals are TTL compatible.
The 8254 Timer / Counter Chip
The Intel (NEC) 8254 contains three independent, programmable, multi-mode
16 bit counter/timers. The three independent 16 bit counters can be clocked
at rates from DC to 5 MHz. Each counter can be individually programmed
with 6 different operating modes by appropriately formatted control words.
The most commonly uses for the 8254 in microprocessor based system are:
z programmable baud rate generator
z event counter
z binary rate multiplier
z real-time clock
z digital one-shot
z motor control
For more information about the 8254, please refer to the Intel’s website
(http://support.intel.com/support/controllers/peripheral/231164.htm).