System Operation - Raytheon DIDS-400 Series Technical Manual

DIDS-402-2AM13
CENTRAL
CPU
MODEL
PROCESSING I/O
402-2AM13
UNIT
CONTROLLER
DISPLAY
TERMINAL
A. SINGLE TERMINAL CONFIGURATION
CPU
FROM 1 TO 64
CENTRAL I/O
MODEL
PROCESSING
CONTROLLER
402-2AM13
UNIT
WITH
DISPLAY
MUL TlPLEXER
TERMINALS
DIDS 68-501
B. MULTITERMINAL CONFIGURATION
Figure 4-1.
Typical System Configuration
All message preparation and editing is accomplished off-line, and the
Display Terminal is connected to the CPU only during periods of actual data
transfer. This feature provides economic operation by conserving CPU time.
The transfer of data between the Display Terminal and the CPU is asynchronous
-and occurs at a rate of 1200 baud. The necessary start, stop, and parity bits are
generated internally by the communications control logic during specific bit times
of each character.
4-4 SYSTEM OPERATION
The Display Terminal operates in either the enquiry-response or the polling
conversational mode. The basic difference between the modes is that the
former provides operator control over data transfers while in the latter, data
transfers are controlled by the CPU.
In either mode .. display terminal operators
generally initiate data messages by operating specific keys on the keyboard. (An
exception is the No Business message which is produced internally without the
operator's knowledge.) Each character key depre ssion enters a specific 7 -bit
digital code in memory and displays a corre sponding character on the CRT
screen. When the entire message text has been composed, the operator initiates
a transmission sequence by depressing the appropriate keys on the keyboard.
In a system configured for the enquiry-response conversational mode, the
mes sage is transmitted to the CPU as soon as the Display Terminal receive s a
clearance to transmit. In polling systems, however, the CPU must poll the
Display Terminal before a data transfer occurs.
The preceding text has briefly described display terminal operation in the
transmit mode. In the receive mode, display terminal operation is again deter-
mined by the conversational mode employed. In enquiry-response systems, the
display terminal operator usually issues an enquiry to elicit a response from the
CPU.
In polling systems, the CPU can issue a write directive at any time to
display a message on the display terminal screen.
4-2