### EIA-422 Eight-Wire Synchronous Modem Wiring

#### Host Adapter to Modem

C/X or EPC/X Host Adapter (HD-15 Male) |  | EIA-422 Synchronous Modem (DB-37 Male)
--- | --- | ---
Signal | Pin | Pin | Signal
RxD- | 1 | Connected to | 6 | RD-
RxD+ | 2 | Connected to | 24 | RD+
RxC- | 4 | Connected to | 8 | RT-
RxC+ | 5 | Connected to | 26 | RT+
TxD- | 6 | Connected to | 4 | SD-
TxD+ | 7 | Connected to | 22 | SD+
TxC- | 9 | Connected to | 5 | ST-
TxC+ | 10 | Connected to | 23 | ST+
GND | 12 | Connected (via shield) to | 19 | GND

#### Modem to Concentrator

EIA-422 Synchronous Modem (DB-37 Male) |  | Concentrator "Host Adapter" Port (HD-15 Female)
--- | --- | ---
Signal | Pin | Pin | Signal
RD- | 6 | Connected to | 6 | RxD-
RD+ | 24 | Connected to | 7 | RxD+
RT- | 8 | Connected to | 9 | RxC-
RT+ | 26 | Connected to | 10 | RxC+
SD- | 4 | Connected to | 1 | TxD-
SD+ | 22 | Connected to | 2 | TxD+
ST- | 5 | Connected to | 4 | TxC-
ST+ | 23 | Connected to | 5 | TxC+
GND | 19 | Connected (via shield) to | 12 | GND

The EIA-422 Synchronous Modem cables are twisted pair cables, each having an HD-15 (high-density DB-15) connector at one end and a DB-37 connector at the other end. The cable should be shielded, and the shield must be connected as shown in the diagram.