DeviceMaster Software Developer Kit Testing Serial Ports
With a loopback plug connected to a port, the loop command may be used to run a loop-back test in either internal loop-back mode, RS-232 mode or RS-422 mode. In RS-232 mode, modem control lines are also tested. In RS-422 mode and internal loop-back mode, only data paths are tested. If the test fails, a hexadecimal error code is displayed. The first digit of the error code indicates what portion of the test failed. Loop-back error codes are shown in the table below.
Examples of loopback test commands are shown below.
Some DeviceMaster models have internal loopback hardware for use by the loop command.
For models that do not support the loopback command for RS-485 ports an RS-485 cross-over cable must be connected between two different ports on the DeviceMaster.
The t485 command is used to perform a bi-directional, half-duplex, data-transfer test between two ports. If ports 0 and 4 are connected with an RS-485 crossover cable, the command to perform the test is:
RedBoot> t485 0 4
Testing ports not connected to each other results in a failure:
RedBoot> t485 0 1
- Failed 485 test: 1220008
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