When the serial port is configured to “No Flow Control,” only Transmit and Ground connections are required. Pin 7 and Pin 8 need to be connected only if other serial flow control types are selected.

Pin 6 is connected only between multiple Whozz Calling? units and acts as a control line. When units are not transmitting data this line resides at -9 VDC. Upon transmit, the unit pulls this line to +9 VDC. Other Whozz Calling? units connected will detect this as a busy condition and will not transmit until the line returns to -9 VDC.

If connecting to a 25 pin serial port on the computer, we suggest using a 9 to 25 pin serial adapter. The pin outs on a 25 pin serial port are not the same as a 9 pin port. When the serial port is configured to “No Flow Control”, only Transmit and Ground connections are required. Request to Send and Clear to Send connections will need to be connected only if other serial flow control types are selected.