ADLINK ACL-8454/12 - Manual (Page 59)

High-Level Programming • 51
Appendix B Timer/Counter
Operation
The ACL-8454 has at most four 8254 chips on board. Refer to section 2.8
for the signal connection and the configuration of these counters. The
following sections are some brief concepts of the 8254 chip.
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:
• programmable baud rate generator
• event
counter
• binary rate multiplier
• real-time
clock
• digital one-shot
• motor control
I/O Address
Each 8254 on ACL-8454 occupies 4 I/O address as shown below.
BASE + 0 LSB OR MSB OF COUNTER 0
BASE + 1 LSB OR MSB OF COUNTER 1
BASE + 2 LSB OR MSB OF COUNTER 2
BASE + 3 CONTROL BYTE
Although there are at most four 8254 chips can be installed, however, only
one chip can be selected at the same time. The programming of 8254 is
controlled by the registers BASE+0 to BASE+3. For more detailed
information, please refer to Intel's data sheet of 8254 chip (see
“http://support.intel.com/support/controllers/peripheral/231164.htm”).