Plato Communications Interface; Plato Receiver; Word Format; Word Polarity - Control Data Corporation INFORMATION SYSTEMS TERMINAL II Hardware Maintenance Manual

PLATO Communications Interface
This interface enables the terminal logic to communicate
with the PLA!O system and discussion here centers on the
signals, pinouts, parameter selection, and operation of the
PLATO Receiver and PLATO Transmitter.
PLATO Receiver
Important aspects of the PLATO Receiver are word format,
word polarity, word parity, data rate, and data assembly/
transfer.
Word Format - The asynchronous PLATO receiver receives 21
bits of serial data after detection of a Start bit (includ-
ing the Start bit). After reception of the 21 bits it
searches for another Start bit. If the bit following a
2l-bit word is a logical 1, it is interpreted as a Start
bit and 21 more bits are clocked in. If after 21 bits, the
incoming data is a logical 0, the receiver stops in Search
mode until the incoming data line switches from
0
to 1, at
which point the receiver resumes its activity. Figure 4-3
shows the receiver word format.
S
T
A
R
T
SHIFT DIRECTION
•
...... - - - - - - - - 2 0 DATA BITS---------------<~
...... ----------IWORD=2IBITS-------------~
Figure 4-3. Receiver Word Format
Word Polarity - The Start bit must be a logical 1 to trig-
ger receiver activity. A logical 1 is received when the
RS-232-C receiver (RJl-3) is in the space condition or the
interface receiver (AJ5-7) is in the space or TTL high con-
dition (both interfaces require that the long line inter-
face not be enabled), or the long line receiver on and the
long line interface enabled.
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