### EIA-232 Eight-Wire Synchronous Modem Wiring

#### Host Adapter to Modem

C/X or EPC/X Host Adapter (HD-15 Male) |  | EIA-232 Synchronous Modem (DB-25 Male)
--- | --- | ---
Signal | Pin | Pin | Signal
RxD | 1 | Connected to | 3 | RxD
RxC- | 4 | Connected to | 17 | RxC
TxD- | 6 | Connected to | 2 | TxD
TxC | 9 | Connected to | 15 | TxC
GND | 12 | Connected (via shield) to | 7 | SG
Jumpered at modem end | 4, 6, 10 | RTS, DSR, DTR
RxC+ | 5 | Connect to pin 4 via capacitor (see below)
TxC+ | 10 | Connect to pin 6 via capacitor (see below)

#### Modem to Concentrator

EIA-232 Synchronous Modem (DB-25 Male) |  | Concentrator "Host Adapter" Port (HD-15 Female)
--- | --- | ---
Signal | Pin | Pin | Signal
RxD | 3 | Connected to | 6 | RxD
RxC | 17 | Connected to | 9 | RxC-
TxD | 2 | Connected to | 1 | TxD-
TxC | 15 | Connected to | 4 | TxC
SG | 7 | Connected (via shield) to | 12 | GND
RTS, DSR, DTR | 4, 6, 10 | Jumpered at modem end
Connect to pin 9 via capacitor (see below) | 10 | RxC+
Connect to pin 4 via capacitor (see below) | 5 | TxC+

To connect host adapters and concentrators to EIA-232 synchronous modems, use the special cables shown in the diagram. Four 2200 pF capacitors (X7R 50V type) are required--two for the host adapter, and two for the concentrator. Install the capacitors between the positive and negative leads of the TxC and RxC signals on the back of the HD-15 connectors.

The EIA-232 wiring feature is not supported by device driver software released prior to 9/1/92. Older releases support only EIA-422 wiring. Only the negative lead for each EIA-422 signal is used in this configuration. The positive lead is left "floating."

The synchronous cables provided by Digi with the concentrators are Eight-Wire Direct (EIA-422) cables. This is the standard method for connecting concentrators to Host Adapter synchronous lines, and to other concentrators.

Eight-Wire Direct cables provide transmit and receive data signals plus discrete clock signals for transmit and receive data. This permits synchronous data rates of up to 10 megabaud, which results in the maximum data throughput under moderate to heavy loads.

The Eight-Wire Direct cable is a twisted pair cable with a male HD-15 (high-density DB-15) connector at one end and a female HD-15 at the other end. The cable should be shielded, and the shield must be connected to the HD-15 connector shell at both ends.

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