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Message Validation
CCM Acknowledgement
of all Messages
Program Validation
of all Messages
CCM Acknowledgement
of T ra nsaction
o
Messages
Signal Characteristics
Transmitted
Signals
Received Signals
70/724 EDGE
Demodulator/Buffer
•
The EDGE System requires that each message, transmitted from an
Input Station, be checked, and that each valid message cause a Message
Acknowledged signal (AB2) to be returned to the EDGE Input Station. Three
methods of checking are permitted o Any combination may be used in an
EDGE System, but only one method can be employed for each Line Con-
centrator and its associated Edge Demodulator/Buffers. In all cases, the
buffer generates the AB2 signal upon receipt of an ACKC from the CCM.
•
Each character is checked for correct parity, and upon detection of
the End Message (EM) character, the CCM generates ACKC to the Edge
Demodulator/Buffer if no error was detected.
•
Each character is checked for correct parity by the CCM, and upon
detection of EM, the CCM transfers validation responsibilities to the
program.
If
the message is acceptable, the program generates an Acknowl-
edge Write Control to the CCM, and then to the Edge Demodulator/Buffero
This method of operation requires that the Input Stations which the buffer
services be equipped with the Delayed Retransmission Option - Feature 438.
•
If
the transaction code of a message is 0, indicating an attendance
recording, the CCM generates an ACKC immediately upon detection of the
EM provided no parity errors have been detectedo Program Validation is
used for all messages which are not identified as transaction 0 trans-
missions. This method of operation requires that all Input Stations which
the Edge Demodulator/Buffer services be equipped with the Delayed
Retransmission Option - Feature 438.
•
The EDGE System controls data flow via specific ac and dc signals
which are initiated at specifiC times or under certain circumstances.
•
The following signals are transmitted by the Edge Demodulator/Buffer
to the Line Concentrator or to the Input Stations o These three signals com-
prise the total transmitting capabilities of the buffer.
Ready - DC Signal -
The Edge Demodulator /Buffer indicates a ready
condition to the Line Concentrator by means of a dc contact closure.
ABl andAB2 - AC Signals -
The Edge Demodulator/Buffer transmits
the Permission to Transmit - AB1, and Message Acknowledged - AB2
signals to the Input Stations. These signals are identical and consist of 20
±
5 ms of unmodulated, signal carrier with a frequency of 2000 cycles.
• Request to Transmit (RT) -
DC Signal - The Edge Demodulator/
Buffer recognizes that an Input Station has been connected to it within 21
ms after the Line Concentrator closes the "Request to Transmit" (RT)
contact.
This contact remains closed as long as the Input Station is con-
nected.
21 ms after the RT contact opens, the buffer recognizes that the
Input Station has been disconnected.
Data - A
C
Signals -
The Edge Demodulator/Buffer accepts data in the
form of a 2000 cycle carrier Signal, modulated at a rate of 250 bits per
second.
4-37
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