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 10M bps, 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.