Black Box MD1640A, MD1641A manual Flow Control Commands, Error Correction/300bps $E

CHAPTER 5: Command Mode

V.42 Error Correction/300bps $E

At 300 bps, error correction is not typically used. $E1 lets the Series II Modem function at 300 bps in either Normal (&E0), Auto-Reliable (&E1) or Reliable (&E2) mode. $E0, which is the Modem’s default, disables 300 bps/V.42 error correction altogether.

AT$E0 = No V.42 Error correction at 300 bps.

AT$E1 = V.42 Error Correction at 300 bps.

The factory default setting is $E0.

5.4.9 Flow Control Commands

Flow control refers to the techniques used by computer devices to stop and restart the flow of data to and from each other. Flow control is necessary so that a device does not receive more data than it can handle. In the case of the Series II Modem, there is a need for flow control in both directions. As illustrated on the next page, flow control for data passing from your computer to the modem is called Modem- Initiated Flow Control and flow control for data passing from the modem to your computer is called Computer/Terminal-Initiated Pacing.

The Series II Modem supports both hardware and software Modem Initiated Flow Control. On the Computer/Terminal-Initiated Pacing side, it supports hardware and software flow control, and a special version used by Hewlett-Packard®compatible systems called ENQ/ACK Pacing. The Modem allows hardware and software pacing to be passed through the modem to the other end of the link so that your computer or terminal can control data start/stop activity through your modem.

This is called Xon/Xoff Pass-Through. To state it simply, “Flow Control” is something the modem does to the computer, while “Pacing” is something the computer does to the modem.

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