Use this information to determine the proper EIA-232 cable requirements for your application.
EIA-232 serial interface cables should be shielded, low capacitance cables, designed specifically for serial data transmission.
EIA-232 interface cables should have the shield grounded at both ends of the cable. Digi recommends Chassis Ground, available on the shell of Digi's DB-25 connectors, and pin 4 of a 10-pin RJ-45 connector.
While good shielding provides reasonable protection against "noise" (electromagnetic interference, or EMI), cables should still be routed away from noise sources wherever possible. Avoid laying cables in close proximity to transformers, generators, motors, fluorescent lights, etc.
The maximum date rate that can be used for EIA-232 connections is primarily determined by the quality and length of the interconnecting cable. The quality of the cable (for transmission purposes) is generally determined by the capacitance per foot rating of the cable.
The following table gives the recommended maximum cable length for a given data rate. Longer cables may be implemented at your discretion.
| Data Rate (bps) | Maximum Cable Length |
| 57,600 or less | 100 feet |
| 115,200 | 80 feet |
| 230,400 | 40 feet |
| 460,800 | 20 feet |
| 921,600 | 10 feet |
Notes:
The maximum length is the amount of cable that is connected to a Digi supplied interconnect device, such as Quad or Octa cables and boxes.
The maximum length is based on a cable rated at:
12.3 pF/foot, conductor to conductor
22.4 pF/foot conductor to shield
In situations where low-capacitance cable is unavailable, or very long cable runs are required, "short-haul" modems can be used to increase the effective range of the EIA-232 interface. Short-haul modems are similar to standard modems, except that they are connected directly to each other via a cable instead of going through a telephone circuit.
Note: Use only externally-powered short-haul modems with Digi products.
If transmission errors occur, follow this procedure to determine the cause of the problem: