U-90E
Data/Fax
Modem
Error Control and Data Compression
9-3
9.3 Flow
Control
This feature refers to stopping and restarting the flow of data into and out of the modem’s
transmission and receiving data buffers. Flow control is necessary so that a device does
not receive more data than it can handle. The U90E provide two kinds of flow control
methods.
9.3.1 Hardware CTS/RTS Flow Control
This is a bi-directional flow control. CTS and RTS are RS232 signals which are available
on your computer. When the modem’s transmission buffer is almost full, The modem will
drop CTS to signal the DTE that it cannot accept any more data. Turn On the CTS to
notify the DTE that it can keep sending data to the modem. On the computer software
side, when the receiving buffer of the software is almost full,it will drop RTS to signal the
modem to stop sending data to the DTE. Turn ON the RTS and the modem will start
sending data again to DTE.
9.3.2 Software
XON/XOFF Flow Control
This is a bi-directional flow control. XON and XOFF character defaults are decimals 17
and 19.These can be changed by modifying the S-Registers 31 and 32.Both the modem
and the DTE will treat XOFF as a signal to stop transmitting data and will treat XON as a
signal to restart sending data. Modems will not send these characters received from the
local DTE to the remote modem.
