Specifications

RS-422/485 Application Note 11
© Copyright B&B Electronics -- Revised 2506
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph 353-91-792444 – Fax [phone]
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.
12 RS-422/485 Application Note
© Copyright B&B Electronics -- Revised 2506
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax [phone]
B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph 353-91-792444 – Fax [phone]
Figure 1.9