Introduction to Data Communications
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18. RS-232D Flow Control

Flow control is the communication between the data transmitter and data receiver to determine whose turn it is to talk. Another name for flow control is handshaking. Flow control is the exchange of predetermined codes and signals between two devices to establish and maintain a connection.

Modem flow control is used between the PC and modem to determine if the modem is ready to receive data from the terminal, if carrier is present, if the line is ringing, etc....

Source to Destination (End to End) flow control

Source to destination flow control is used to control the data communication from the sendor to the receiver. It may or may not have a modem involved. Source to destination may involve direct PC to PC communication or PC to Serial Printer communication. It is also called end to end flow control.

DTE-DCE Flow Control

There are 2 basic types of DTE-DCE Flow Control used with RS-232D connections:

18a. Hardware Handshaking

Hardware Handshaking uses the physical signals in the RS-232D cable such as RTS, CTS, DSR and TSR to control the flow of data. Hardware Handshaking is used primarily with modems: PC to modem connection or terminal to modem connection.

Introduction to Data Communications
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