User manual

Section 6

DATA TRANSFER

6-5

6.5 Error Free or Not at All

In some applications you may need to be sure you connect with error control invoked. It

may be desirable not to connect at all if you cannot establish a reliable link. Setting AT&E1

and AT&I0 achieves this. If the remote modem cannot support MNP, the DPX-213 will

terminate the call immediately after the MNP negotiation sequence.

If AT&E1 and AT&I1 are set, the DPX-213 will negotiate with the remote modem for the

highest level of MNP that both support and if no MNP support is found, the modem will

enter the Transparent Data Mode and remain on-line.

6.6 Constant Speed Interface

A Constant Speed Interface on the DPX-213 can be invoked to ensure your terminal

always functions at the same speed, regardless of the line speed the modem connects at.

If you want the interface speed to change with each different line speed, use the AT&I0

command. For example, with AT&I0 set, if you have your terminal set at 4800 bps then

call a 1200 bps modem, the DPX-213 will issue the message "CONNECT 1200" at the

initial bit rate of 4800 bps and then immediately switch to 1200 bps for the remainder of

the call. To make any sense of the data you must quickly change your terminal speed to

1200 bps.

Some software packages, such as Telix, can read the CONNECT (speed) message and

automatically adjust the PC com ports while in other packages you must manually reset the

PC com port speed. If the interface constant speed rate is set at 4800 bps for example, the

"CONNECT 2400" message could incorrectly instruct your software into changing the

terminal speed to 2400 bps when the correct speed is 4800 bps. We recommend the use of

the Constant Speed Interface provided your terminal can employ either hardware of

software flow control.

6.7 File Transfer Restrictions

File transfer restrictions exist when using Xon/Xoff flow control. For example, when

transferring pure binary files, where the data bytes in the file may be any combination of 8

bits, there is a possibility there will be some stray Xon or Xoff characters. If Xon/off flow

control (AT&K1) or AT&U1,2 or 3 is enabled, any stray Xoff characters will command the

DPX-213 to stop sending data.

For such applications, the DPX-213 should be set to RTS/CTS flow control with the

AT&K2 command. This command will work for text or binary files provided your

communications software correctly drives RTS and respond to CTS. MNP still works with

binary files and ignore any embedded Xon/Xoff characters. Alternatively, a file transfer

program such as Zmodem (that removes the Xon/Xoff characters at the sending end and

adds them back at the receiving end) is required.