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Chapter 5
FUNCTIONAL DESCRIPTION
5.1 INTRODUCTION.
This chapter contains an overall functional description
of the Model 950 terminal. The description is based on a
simplified block diagram. The description is written to
provide the advanced systems user with a general under-
standing of the operation of the Model 950 in terms of its
hardware major circuits.
5.2 TERMINAL OVERVIEW.
The Model 950 hardware consists of the following nine
major circuit areas (see Figure 5-1):
Display processor
Printer port interface circuits
Display generator
Keyboard interface circuits
Video Module
Keyboard circuits
Screen
Power supply.
Main port interface
circuits
These circuits are described in the following paragraphs.
5.3 DISPLAY PROCESSOR.
The display processor is the main controller of the Model
950.
It
contains the microprocessor central processing
unit (CPU) and most of the terminal memory. The CPU
responds to input either from the host or from the key-
board by instructions from ROM in the terminal and
then performing the action indicated by the instruction.
The memory in the display processor consists of both
Read Only Memory (ROM) and Random Access Mem-
ory (RAM). The ROM contains the program instruc-
KEYBOARD
TO
HOST
COMPUTER
TO
SERIAL
DEVICE
P1 I
I
I
I
I
SERIAL:
DATA
I
I
P3
I
I
I
SERIAL
I
DATA
I
I
P4
I
I
I
SERIAL
I
DATA
I
KEYBOARD
<=-
INTERFACE
CIRCUITS
Y
MAIN
; '
DISPLAY
INTERFACE
<
;>
PROCESSOR
PORT
"
ir>
PRINTER
<=-
INTERFACE
PORT
tions for controlling the CPU; the RAM provides the
CPU with temporary storage space for computation
variables.
The display processor contains the system clock circuits
for timing all the functions of the terminal. It also con-
tains input/ output drivers for handling data to and from
the host (main) and the printer ports.
5.4 KEYBOARD AND KEYBOARD INTERFACE
CIRCUITS.
The keyboard is a device for transmitting serial data to
the display processor. Each of the keys are switches.
When closed, these switches are sensed by circuits that
send a code (that corresponds to the key pressed) to the
display processor. Keyboard interface circuits convert
the keyboard serial data to parallel for input to the dis-
play processor circuits.
5.5 MAIN INTERFACE PORT.
The main interface port, consisting of P3 and interface
circuits, receives and transmits serial RS-232C data be-
tween the host computer and the display processor. This
port may be connected either directly to a local computer
(as in an application dedicated to a microcomputer
system) or to a modem for communicating with a distant
computer. The interface circuits convert the input serial
data to parallel for application to the display processor;
these circuits convert output data from parallel to serial
RS-232C format for transmission to the host.
5.6 PRINTER PORT INTERFACE.
The printer port interface, consisting of P4 and interface
circuits, performs the identical function for the printer
r: ;)
DISPLAY
VIDEO
SCREEN
GENERATOR
MODULE
TO ALL
CIRCUITS
115/230 VAC
115
or
230 VAC
POWER
SUPPLY
FUSE
FUSE
Figure 5-1
Model 950 Simplified Block Diagram
5·-35
.....
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