XR16M890IL32-0C Datasheet, PDF (40/63 Pages) Exar Corporation – UART WITH 128-BYTE FIFO AND INTEGRATED LEVEL SHIFTERS

XR16M890
UART WITH 128-BYTE FIFO AND INTEGRATED LEVEL SHIFTERS
REV. 1.0.0
3.9 Setup/Hysteresis Register (SHR) - Write Only
In the Auto RS-485 half-duplex mode, the RTS# control output can be asserted from 0 to 15 bit times before
data is transmitted to allow for the startup time of an RS-485 transceiver that may be in shutdown mode. The
RTS# control output can also be delayed from 0 to 15 bit times after the last byte has been transmitted to allow
the data to propogate down long data cables.
In the Auto RTS flow control mode, this register selects the hysteresis levels that will be used with
programmable trigger levels (Trigger Table-D).
SHR[3:0]: RS-485 Turn-Around Delay / Auto RTS Hysteresis
When the Auto RS-485 half-duplex mode is enabled (FCTR[3] = 1), the value programmed in these bits will be
the number of bits (0-15) the RTS# pin will wait before it is de-asserted after the last byte that has been
transmitted.
When Auto RTS flow control is enabled (EFR[6] = 1) and programmable trigger levels are used (FCTR[5:4] =
’11’), these bits select the hysteresis levels for the RTS# flow control pin (See Table 13).
TABLE 13: AUTO RTS HYSTERESIS
SHR BIT-3
SHR BIT-2
SHR BIT-1
SHR BIT-0
RTS# HYSTERESIS
(CHARACTERS)
0
0
0
0
0
0
0
0
1
±4
0
0
1
0
±6
0
0
1
1
±8
0
1
0
0
±8
0
1
0
1
±16
0
1
1
0
±24
0
1
1
1
±32
1
0
0
0
±40
1
0
0
1
±44
1
0
1
0
±48
1
0
1
1
±52
1
1
0
0
±12
1
1
0
1
±20
1
1
1
0
±28
1
1
1
1
±36
SHR[7:4]: RS-485 Setup Delay
When the Auto RS-485 half-duplex mode is enabled (FCTR[3] = 1), the value programmed in these bits will be
the number of bits (0-15) the RTS# pin is asserted before the first byte is transmitted.
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