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2270 Fiber Optic Modem
Table 3-C. RS-499 (RS-422) Signals and Pin Assignments
pin EIA signal name CCITT signal direction
1 FG Frame Ground 101 frame ground
19 SG Signal Ground 102 signal ground
4/22 SD Send Data 103 to modem
5/23 ST/SCT Send Timing 114 from modem
6/24 RD Receive Data 104 from modem
7/25 RS/RTS (b,c,d,e) Request To Send 105 to modem
8/26 RT/SCR Receive Timing 115 from modem
9/27 CS/CTS (d,e) Clear To Send 106 from modem
10 LL/LT (a) Local Loopback Test 141 to modem
13/31 RR/DCD (e) Receiver Ready /
Data Carrier Detect 109 from modem
14 RL/RT (a) Remote System Test 140 to modem
17/35 TT/SCTE Terminal Timing 113 to modem
11/29 DM/DSR Data Mode/Data Set
Ready 107
a. The 2270 Modem includes a built-in Loopback Test feature. Two normal test lines (RS-422 pins 10 and 14) are
used for this interface loop. Refer to Chapter 5, Troubleshooting, for a more thorough description of this
feature.
b. Model -22: Request To Send is held low when there is no connection or the interface connection is removed.
c. Model -H22: Request To Send is held high when the users device does not supply an RS input or the interface
connection is removed.
d. Model - R2R: Request To Send is held low as with the -22. Clear To Send is provided as a balanced output.
e. Only local handshake is supported.
3.3.1 Model -22
The RS input control is biased to the OFF (negative voltage) state. If a connection is not made to
this line, the CS control output from the modem will drive to the OFF state.
3.3.2 Model -H22
The specific difference between the -H22 model and the standard -22 model is that the RS input
control is biased to the ON (positive voltage) state. If a connection is not made to this line, the CS
control output from the modem will drive to the ON state.
3.3.3 Model -R2R
The RS input control is biased to the OFF (negative voltage) state. If a connection is not made to
this line, the CS control output from the modem will drive to the OFF state.
This interface provides the Clear to Send (CS) control as balanced output (using two leads).