Contec COM-1PDH-LPE, User Manual, Page: 36 / 45

4. Functions
COM-1PDH-LPE
31
Automatic RTS Control Functions
This function applies to half duplex mode communications.
As half duplex means that the same line is used for sending and receiving, the RTS and CTS signals are
used to switch between sending and receiving. Normally, RTS is set by writing to the corresponding
register bit, but on this board it is controlled by hardware. This reduces the load on the CPU.
If you wish to use this function with the "Standard COM Driver Software COM Setup Disk" from the
bundled disk, it can be specified by the user application.
Visual C++
Use the SetCommState() Win32 communications API routine to set [RTS_CONTROL_TOGGLE
(0x03)] in the fRtsControl member of the DCB structure.
In Visual Basic, half duplex communication cannot be used via the communication control
(MSComm) as MSComm does not support setting this function.
Other Functions
Bus Isolation
Between PCs are electrically isolated from each other.
As isolation of the bus is provided, this prevents electrical interference between the PC and external
circuits. This means you can safely use the boards in environments where noise is likely to be generated
on the communication lines and where you are concerned about this causing incorrect operation or
damage to the PC.
Surge Protection
As surge protection is provided on all RS-422A/485 control lines, you can safely use the boards in
environments where you are concerned about surges causing incorrect operation or damage to the PC.
CAUTION