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accordance with system requirements.
The 20 bit word transmitted (received) consists of an 18
bit word from the DATANET-30 memory plus one parity bit and one control bit generated by the
transmitting DA TANET-30.
The sequence of transmit and receive for the WBC is the same as for the character buffer channel
except for the automatic addition of the parity and control bits to the transmitted word.
Character/Word Unit Module (CWU 931)
The Character/Word Unit module CWU 931 occupies one module space and is similar to CWU 930
except that characters are transmitted and received on a character synchronous basis. The
character/word unit module (CWU 930) can contain two character buffer channels (CBC 931).
A code level plug is required for each CBC 931.
CHARACTER BUFFER CHANNEL (CBC 931). One buffer channel provides the interface between
the DA TANET-30 and a half-duplex transmission line.
The CBC is synchronized by the digital
subset connected to the transmission line and therefore does not require a timing connector plug.
The buff er control unit contains hardware to control the character length as defined by the code
level plug.
Buffers in a module may be operating at different character lengths. The buffer
channel operates with a character oriented device at speeds determined by the subset and remote
terminal.
A synchronous digital subset must be on each end of the transmission line.
The
standard bit rates are 2000 and 2400 bits per second.
The code level may be from 5- to 16-bit codes with character synchronization (no start/ stop bits).
The code level (character length) is selected or changed by a code level plug for each CBC. By
changing code level plugs, the code level may be varied to meet different remote terminal
operations or programming techniques.
The code level plug also defines the bit configuration of the synchronizing character, the number
of bits per character, and where the receive lines will enter the data bits into the "working"
register (A or B register); that is, the high- or low-order position of the A or B register. The
code level plug can be arranged to accept two characters (8 level} before setting the receive flag.
Also, the code level plug can be arranged to mask off a bit. The line interface is Bell System
Dataphone Model 201A or 201B Data Set or equivalent.
Transmit Flag
201A
201A
Data
5
to
16
Transmitting
Data
Data
Shift
Bit
Data
Buffer
Device
Set
Set
Register
Code
Register
Selector
•
Control
Lines
Receive Flag
Figure 18. Character Buffer Channel Block Diagram
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