Serial Port Flow Control - Toshiba V.90 User Manual

The modem card has two kinds of flow control:
❖

Serial port flow control

❖
Modem port flow control (only in reliable mode)
Computer
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.
DTE
t
Transmi
Receive
Serial port
flow control
MNP and V.42
Flow control
Modem
DCE
Phone line
Buffer
Buffer
Modem port
flow control
55
Phone
Circuit