Specifications

Chapter 1 - Overview RS-422 And RS-485 Applications Ebook
Page 21 of 137 Manual Documentation Number: <DocNumber>
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NOTE: For a more complete explanation of biasing refer to Biasing an RS-485 Network (p. 32).
Figure 12: Bit-Wise Enable Timing
For additional details refer to Bit-wise Enable Timing Diagrams (on
page 97).
Other Tri-State Control Techniques
Some RS-485 devices use bit counters or a UART Transmit buffer
status line for control.
Bit counters monitor the number of bits in a message and enable the
RS-485 driver while data bits are being sent, counting the number of
bits sent and disabling the driver when the total number is reached.
The UART transmit buffer status technique uses a signal that is part of
the UART circuitry. When data to be sent is detected the UART control
line enables the RS-485 driver. The UART's transmit buffer stores data
as it is received, and sends it to the RS-485 driver. When the buffer is
empty the UART disables the driver.