User Manual

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Optional External Power
Termination is a critical requirement for port-power devices such as the
TCC-80I. In most circumstances, termination resistors are used when the
RS-422/485 cable length is longer than 100 m. Regardless of how much
the data signal is dissipated, the termination resistors absorb more than
75 mW of power from the power source when TCC-80I is unable to use
the limited serial power. In other words, if long distance RS-422/485
transmission or termination is required, then an external USB power cord
or DC power supply should be used (in this case, DIP SW3 must be ON).
By testing the TCC-80I at different baudrates and transmission distances,
we have determined the maximum transmission distance that can be
achieved when using serial port power. The test results are shown in the
following table.