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2.4.5 Settings for Balanced/Unbalanced Outputs
The conversion from Balanced to Unbalanced output data streams is accomplished using
jumper JP11, which is a 24-pin jumper network. For MIL-STD-188-114 Balanced (RS-422
compatible) output, JP11 connects the following pins together: 2-23, 4-21, 6-19, 8-17, 10-15,
and 12-13. When a change to MIL-STD-188-114 Unbalanced (RS-423 compatible) output is
desired, JP11 must be removed, rotated 180 degrees, and reinserted so that the following pins are
connected: 1-24, 3-22, 5-20, 7-18, 9-16, and 11-14.
2.5 Output
Connections
The F22XX Modem uses a standard DB25 Female connector for the electrical signal
interface. The pinout for this is given in Table 3.
SIGNAL PIN
INTERFACE
TX D (A)
2
INPUT
TX D (B)
14
INPUT
TX CLK (A)
24
INPUT
TX CLK (B)
11
INPUT
DTR (A)
20
INPUT
DTR (B)
23
INPUT
RX D (A)
3
OUTPUT
RX D (B)
16
OUTPUT
RX CLK (A)
17
OUTPUT
RX CLK (B)
9
OUTPUT
DSR (A)
6
OUTPUT
DSR (B)
22
OUTPUT
DCD (A)
8
CONNECTED INTERNALLY TO DSR (A)
DCD (B)
10
CONNECTED INTERNALLY TO DSR (B)
TABLE 3. MODEL F22XX ELECTRICAL SIGNAL INTERFACE (DB25F) PINOUT
2.6 LOOPBACK
The F22XX Modem has a loopback mode to facilitate the testing of the unit in a system
environment. When the Loopback switch on the front panel of the circuit card is in the ON
position, the line encoder is routed directly to the line decoder, and the fiber optic receiver output
is connected directly to the fiber optic transmitter input. This achieves a loopback of the
transmit data to the receive data output, the transmit clock to the receive clock output, the DTR
input to the DCD/DSR output, and the received optical input to the transmit optical output.
Therefore the loopback mode tests virtually 100% of the Modem.
