Allied Data Technologies TRON SECURE 33.6, Руководство пользователя

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6 SPECIAL APPLICATIONS
This chapter explains what a Speed convertor is, what it can do and how the flow control works
in this. Speed convertor and flow control are necessary with an MNP or V42 connection. Error
correction and data compression are roughly discussed. The following subjects are also
discussed: Leased line operation, Remote configuration and Auto- dialback.
6.1 Full Speed adaption
The full speed adaption in the TRON Secure 33.6 modems causes the data speed to the RS232
connection of the modem to be independent of the data speed of the telephone line.
Communication with the computer now takes place on a fixed baudrate of 115,200 bps at the most,
irrespective of the speed of the telephone line. The required communication speed is set with the
AT+MS command. During a connection the established line speed can be read from the LED on
the front panel of the modem.
The combination of full speed adaption and automatic baudrate selection in the auto answer
mode makes is possible to establish a data connection at an arbitrary speed without having to
adjust the DTE-speed in the software.
6.2 Automatic flow control
When the modem uses a speed convertor, there is a difference in speed between the serial port
and the telephone line. This means that the modem receives data faster than it can send through
the telephone line. The information is therefore temporarily stored in a buffer.
There are two ways for a modem to indicate that the computer has to stop sending information
for a while because the buffer is in danger of overflowing:
1. By making CTS (Clear To Send) on the RS232C port inactive
2. By means of the Xon/Xoff protocol
The AT&K command can be used to select the flowcontrol options.
This is how CTS/RTS flowcontrol works:
As soon as the buffer is almost full, CTS is made inactive. When the computer recognizes this CTS
flow control, it reacts to it by no longer sending data to the modem. When the buffer is empty, CTS
is made active and the computer can start sending new bytes to the modem.
The computer can also signal the modem to stop sending data, it uses the RTS signal for this
purpose.
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