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2.4.3
MODEL 971 - 280 PROCESSOR BOARD
GENERAL DESCRIPTION
The 971 Processor Board is the Central Processing Unit (CPU) of IMS
International systems.
This board controls the rest of the system.
The heart of the 971 board is the 2-80A microprocessor.
The 2-80 has 158
instructions with a 1 msec instruction cycle time.
It has a 16-bit address bus,
which means it can address 64 Kbytes of memory directly, and an 8-bit data bus.
It can address 256 bi-directional I/O ports and has priority vectored interrupts.
Interrupts are used so a device can signal the CPU for attention, instead of
waiting for the CPU to poll it.
There are eight different levels of interrupts,
each with a different priority.
They are labeled Vector Interrupt 1 to Vector
Interrupt 7 (VIO-VI7); VIO has the highest priority.
The 971 has a real-time clock in the form of the 58167 integrated circuit.
This
chip has addressable real-time counters which count from tenths of seconds to
months.
The 971 board has two serial ports which are connected, via cables, to the I/O
panel on the back of the machine.
These ports are controlled by the 8250
Asynchronous Communications Controller.
This chip converts the serial data
from the port to parallel data for the system; it also converts parallel data to
serial data to be output to the port.
These ports use the RS -23 2 protocol; for
some connections, wires may need to be exchanged for proper operation.
This board also contains the IMS Intial Program Loader (IPL) boot EPROM.
The
program 1n this EPROM is used when the computer is first turned on or reset.
The Model 971 processor consists of a single Printed Circuit Board that occupies
one slot in the Series 5000 or 8000 Computer Systems. It interfaces with the
rest of the system through the address, data, and control lines of the S-100 bus.
The 971 Processor Board consists of the following function divisions.
• 2-80A 8-bit Microprocessor (CPU)
• Priority Vectored Interrupt Circuitry
• Two Serial RS -23 2C Ports
•
Real-Time Clock
• 2 K/4K/8K by 8-bit EPROM
''''-0/
J
IMS International
5000 Series Microcomputers/7.01.83/page 20
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