Communication functions carry out communications through the serial and parallel I/O ports of the system. Following are the communication functions:
| Function | Description |
| BuildCommDCB | Fills a device control block with control codes. |
| ClearCommBreak | Clears the break state from a communications device. |
| CloseComm | Closes a communications device after transmitting the current buffer. |
| EnableCommNotification | Enables/disables WM_COMMNOTIFY posting to window. |
| EscapeCommFunction | Directs a device to carry out an extended function. |
| FlushComm | Flushes characters from a communications device. |
| GetCommError | Fills a buffer with the communication status. |
| GetCommEventMask | Retrieves and then clears an event mask. |
| GetCommState | Fills a buffer with a device control block. |
| OpenComm | Opens a communications device. |
| ReadComm | Reads the bytes from a communications device into a buffer. |
| SetCommBreak | Sets a break state on a communications device. |
| SetCommEventMask | Retrieves and then sets an event mask on a communications device. |
| SetCommState | Sets a communications device to the state specified by the device control block. |
| TransmitCommChar | Places a character at the head of the transmit queue. |
| UngetCommChar | Specifies which character will be read next. |
| WriteComm | Writes the bytes from a buffer to a communications device. |