SHM-B Async

When in loopback mode, the switch button indicator will appear to the sender. If a CRT terminal is connected to the SHM-B, typing characters on the keyboard should result in the same characters appearing on the CRT screen. If no characters appear, check your EIA-232 connections and the setting of S1. See Figure 3 for an illustration of the loopback mode.

The TD and RD LEDs on the front panel of your SHM-B indicate the status of the SHM-B transmitter and receiver, respectively. Green indicates a LOW EIA-232 level and red indicates a HIGH EIA-232 level. The LEDs will modulate as data is transmitted and received by the SHM-B. Remember that these LEDs are monitoring the actual received and transmitted signals, not the TD and RD lines of the EIA-232 interface.

When the loopback test is completed, press the LOOPBACK switch again to return the SHM-B to normal mode. The switch button indicator should now be black. Data transmission between the two modems will now be possible.

If you experience problems communicating between the two SHM-Bs, use Table 1 to help diagnose the problem.