98 | MNP and V.42 |
Flow control |
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Serial port | Modem port |
flow control | flow control |
Flow control
Serial port flow control
Serial port data flow is controlled by the modem in its communication with a personal computer.
If the serial port speed is higher than the modem port speed, this control function sends a transmission halt request to the personal computer before the buffers in the modem are about to become full. When the buffers have room to receive data again, the transmission halt request is canceled and data transmission from the personal computer is resumed.
The internal modem provides three kinds of serial port flow control: one determined by software and two determined by hardware.
XON/XOFF flow control (software)
Flow control is performed by sending XON and XOFF control codes in the data stream. The XOFF code makes a transmission halt request. The XON code makes a transmission restart request.