Register Structure & Programming
•
25
3.6 Programmable Interval Timer
Note : The material of this section is adopted from
“Intel Microprocessor and Peripheral Handbook Vol. II --Peripheral”
3.6.1 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.
3.6.2 The Control Byte
The 8254 occupies 8 I/O address locations in the ACL-7130 I/O
map. As shown below.
Base + 4
LSB OR MSB OF COUNTER 0
Base + 5
LSB OR MSB OF COUNTER 1
Base + 6
LSB OR MSB OF COUNTER 2
Base + 7
CONTROL BYTE for Chip 0
Before loading or reading any of these individual counters, the
control byte
(Base + 7
)
must be loaded first. The format of
control byte is :
Summary of Contents for ACL-7130
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