ADLINK Technology NuDAQ ACL-8454, Руководство пользователя

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8254 Timer Chip Operation
Appendix 8254 Timer Chip
Operation
The ACL-8454 has at most four interval 8254 chips on board. Refer
to section 3.5 for the signal connection and the configuration of the
counters. The following sections describe the details 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 us es for
the 8254 in microprocessor based system are:
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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 Microsystems
Components Handbook.
I/O Address
The 8254 in the ACL-8454 occupies 4 I/O address as shown below.
Although there are four 8254 chips on board, however, only one chip
is selected in one moment. The programming of 8254 is control by
the registers BASE+0 to BASE+3. The functionality of each register is
specified in the following sections. For more detailed information,
please refer handbook of 8254 chip.
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