Appendix; The Intel (Nec) 8254; The Control Byte - ADLINK Technology cPCI-7300A User Manual

8254 Programmable Interval Timer
Note: The material of this section is adopted from "Intel Micropro-
cessor and Peripheral Handbook Vol. II --Peripheral"

The Intel (NEC) 8254

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
For more information about the 8254, please refer to the NEC
Microprocessors and peripherals or Intel Microprocessor and
Peripheral Handbook.

The Control Byte

The 8254 occupies 8 I/O address locations in the PCI-7300A I/O
map. As shown in the following table:
Base + 0 LSB OR MSB OF COUNTER 0
Base + 4 LSB OR MSB OF COUNTER 1
Base + 8 LSB OR MSB OF COUNTER 2
Base + C
Before loading or reading any of these individual counters, the
control byte (Base + C) must be loaded first. The format of control
byte is:

Appendix

Appendix
CONTROL BYTE for Chip 0
93