DAN-190 Datasheet, PDF (4/6 Pages) Exar Corporation – EXAR UARTS IN RS-485 APPLICATIONS

DAN190
EXAR UARTS IN RS-485 APPLICATIONS
4.4 UARTs with Programmable Turn-Around Delay
Most UARTs with the Automatic RS-485 Half-Duplex Direction control feature change from the TX mode to the
RX mode almost immediately. However, this may be an issue for applications with long cables. Therefore,
some UARTs also have a programmable turn-around delay of 0-15 bits before the control output changes from
the TX mode to the RX mode to allow the signal to propagate to the furthest nodes. The table on the next page
shows the UARTs that have this feature.
TABLE 1: UARTS WITH AUTO RS-485 DIRECTION CONTROL
UART PRODUCT
NUMBER
ST16C650A
XR16L651
XR16C850
XR16C2850
XR16C2852
XR16C864
XR16L2750
XR16L2751
XR16L2752
XR16V2750
XR16V2751
XR16V2752
XR16M2750
XR16M2751
XR16M2752
XR16M752
XR68M752
XR16L784
XR16L788
XR16V598
XR16V698
XR16V794
XR16V798
XR17C152
XR17C154
XR17C158
XR17D152
XR17D154
XR17D158
XR17V252
XR17V254
XR17V258
XR20M1170
XR20M1172
RS-485 CONTROL
OUTPUT
RTS#
RTS#
OP1#
RTS#
RTS#
OP1#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS# or DTR#
RTS#
RTS#
DEFAULT TX
POLARITY
HIGH
HIGH
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
LOW
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
HIGH
INVERT POLARITY
FEATURE
YES
YES
NO
NO
NO
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
YES
YES
ENABLE RS-485
PIN
NO
NO
NO
NO
NO
NO
NO
YES
NO
NO
YES
NO
NO
YES
NO
NO
NO
NO
NO
NO
NO
NO
NO
YES
NO
NO
YES
NO
NO
YES
NO
NO
YES
YES
PROGRAMMABLE
TURN-AROUND
DELAY
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
YES
NO
NO
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