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RS-422/485 Application Note 11

 Copyright B&B Electronics -- Revised October 1997

B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350

PH (815) 433-5100 -- FAX (815) 434-7094

Send Data Control of an RS-485 Device

Many of B&B Electronics’ RS-232 to RS-485 converters and RS-485

serial cards include special circuitry, which is triggered from the data signal to

enable the RS-485 driver. Figure 1.9 is a timing diagram of the important

signals used to control a converter of this type. It is important to note that the

transmit data line is “disabled” at a fixed interval after the last bit, typically

one character length. If this interval is too short, you can miss parts of each

character being sent. If this time is too long, your system may try to turn the

data line around from transmit to receive before the node (with the Send Data

converter) is ready to receive data. If the latter is the case, you will miss

portions (or complete characters) at the beginning of a response.

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B&B Electronics RS-422 Spezifikationen Seite 14