What Is Xon/Xoff?

DocumentID: 647066
Revision Date: 29-Feb-96 8:19:19 PM

The information in this document applies to:
WordPerfect® 5.1 for DOS

Problem

Symptoms: What is Xon/Xoff? Solutions: Xon/Xoff is a protocol used with serial printing. Data is sent to the printer by the program. When the printer's buffer starts to fill, the printer sends a bit to the CPU to tell the program to stop sending data. The program must be smart enough to monitor this and recognize the bit telling it to stop. When the printer's buffer has emptied a little, the printer sends a bit to the CPU to tell the program to start sending data again. This is Xon/Xoff. The only way it will work is if the pin configuration is set up correctly. The CPU and the printer send data on the second pin, and each receives it on the third pin. The program must also be set up to look for the bit being sent to the CPU that tells it to stop sending the data. Hardware Handshaking does the same thing except the program does not need to monitor for the bit. The CPU does this job.

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