Win32 System Services: The Heart of Windows® 98 and Windows® 2000

11.6. Flow Control

The 32-bit APIs supports three different types of flow control:

1. Xon/Xoff (software)

2. RTS/CTS (hardware)

3. DTR/DSR (hardware)

Flow control is used by the comm libraries at both the sending and receiving ends to prevent buffer overflow. When the comm system receives characters, it places them in an input buffer. If the system does not pull characters out of the buffer fast enough to match the rate at which they arrive, then the buffer will fill and eventually overflow. Flow control allows a receiver to send a signal that tells the sender to stop sending characters because of an impending buffer overflow. When the buffer is again clear, the receiver can send another signal to the sender telling it to resume.

Xon/Xoff flow control uses ...