Hardware Handshaking

Hardware Handshaking

The hardware handshake function is configurable using the NI GPIB-Serial Converter Wizard. When Flow Control is set to Hardware, the device enables hardware handshake during serial data transfers and uses the Request to Send (RTS on the GPIB-RS232, RTS+ and RTS– on the GPIB-RS485/RS422) and Clear to Send (CTS on the GPIB-RS232, CTS+ and CTS– on the GPIB-RS485/RS422) signal lines. When the GPIB-RS232/485/422 is ready to accept serial data, it asserts the RTS line(s). RTS remains asserted until the GPIB-RS232/485/422 data buffer is almost full. At this point, the GPIB-RS232/485/422 unasserts the RTS line(s), signaling to the serial host that it is no longer ready to accept data. The serial host should monitor the RTS line(s) and suspend data transmission whenever RTS becomes unasserted. The GPIB-RS232/485/422 asserts RTS when it is again ready to receive serial data.

The GPIB-RS232/485/422 can also suspend transmission when the serial device is no longer ready to accept data. The GPIB-RS232/485/422 is configured to immediately stop transmission of serial data when CTS becomes unasserted. It resumes transmission when CTS is reasserted.

Because most serial devices use the same form of hardware handshaking as the GPIB-RS232/485/422, you can achieve bidirectional flow control by using a serial cable that connects the GPIB-RS232/485/422 RTS signal(s) to the serial device CTS signal(s). In addition, the serial device RTS signal(s) should be connected to the GPIB-RS232/485/422 CTS signal(s). This setup allows each device to monitor the RTS signal(s) of the other device and to suspend transmission when necessary to prevent data loss. Refer to Interfacing to an RS232 Device or Interfacing to an RS485 Device for more information on wiring schemes.

Note  Do not enable hardware handshaking on the GPIB-RS232/485/422 if your serial cable does not support it or you did not properly connect the RTS and CTS signals as described above. Enabling hardware handshaking in this case may prevent the GPIB-RS232/485/422 from sending serial data.

Note  In configuration mode, the GPIB-RS232/485/422 enables hardware handshaking. If your cable does not support hardware handshaking, you may experience problems configuring your hardware.