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CHAPTER 9: TECHNICAL INFORMATION
Functional Description of Interchange Circuits
A list of circuits showing category as well as equivalent CCITT identification in accordance with
CCITT Recommendation V.24 as amended at the VI Plenary Assembly (Geneva, Switzerland, October
1976) is shown in the next table.
Interchange Circuits By Category
Table T:
CCITT
Inter-
Equiv-
change
alent
Circuit
SG
210
202
CRQ
213
PWI
203
DLO
204
DSC
ACR
205
PND
210
DPR
211
206
NB1
207
NB2
208
NB4
209
NB8
Circuit SG - Signal Ground (CCITT 201)
Direction: Not Applicable
This conductor directly connects the DTE circuit ground to the 7500 circuit ground to provide a
conductive path between the DTE and 7500 signal common.
Circuit CRQ - Call Request (CCITT 202)
Direction: TO 7500
The ON condition of this circuit indicates a request to originate a call. The call is aborted if the 7500
detects the OFF condition on Circuit CRQ prior to turning circuit DSC ON.
The OFF condition indicates that the DTE is not using or has completed use of the 7500's ACU
interface.
After the 7500 has turned ON Circuit DSC, the DTE may turn Circuit CRQ OFF without causing a
disconnect.
140
Description
Signal Ground
Call Request
Power Indicator
Data Line Occupied
Distant Station Connected
Abandon Call and Retry
Present Next Digit
Digit Present
Low Order Binary Digit
Second Order Binary Digit
Third Order Binary Digit
High Order Binary Digit
Digit.
Signal
Gnd./
To
To
Common
7500
7500
Return
X
X
X
X
X
X
X
Control
From
7500
X
X
X
X
X
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