XR21B1420 Datasheet, PDF (51/60 Pages) Exar Corporation – Enhanced 1-Ch Full-Speed USB UART

XR21B1420
Bit
1:0
Default
Description
0
CTRL
Note: If configured as CTS input, GPIO5/RTS# must be configured as RTS# output and GPIO2/DSR# and
GPIO3/DTR# must be configured as GPIOs.
00: GPIO7/RS485 is configured as a GPIO input
01: GPIO7/RS485 is configured as a GPIO open drain output
10: GPIO7/RS485 is configured as a GPIO push-pull output
11: GPIO7/RS485 is configured as a push-pull auto. RS-485 half-duplex enable output
PIN_CFG_TXT (0x028) - Read/Write OTP
This register configures the functionality of the GPIO8/TXT pin
Bit
7
6
5:2
1:0
Default
Description
0
PULLUP_EN
This register bit is used to enable the internal pull-up resistor. This setting will be ignored if GPIO8/TXT is con-
figured as an output.
0: Do not enable internal pull-up
1: Enable internal pull-up if configured as an input
0
PULLDOWN_EN
This register bit is used to enable the internal pull-down resistor. This setting will be ignored if GPIO8/TXT is
configured as an output.
0: Do not enable internal pull-down
1: Enable internal pull-down if configured as an input (will not be enabled if Pull up is enabled)
0
RESERVED
These bits are reserved and should be written as ’0’.
0
CTRL
00: GPIO8/TXT is configured as a GPIO input
01: GPIO8/TXT is configured as a GPIO open drain output
10: GPIO8/TXT is configured as a GPIO push-pull output
11: GPIO8/TXT is configured as a push-pull TX toggle output
PIN_CFG_RXT (0x029) - Read/Write OTP
This register configures the functionality of the GPIO9/RXT pin
Bit
7
6
Default
Description
0
PULLUP_EN
This register bit is used to enable the internal pull-up resistor. This setting will be ignored if GPIO9/RXT is con-
figured as an output.
0: Do not enable internal pull-up
1: Enable internal pull-up if configured as an input
0
PULLDOWN_EN
This register bit is used to enable the internal pull-down resistor. This setting will be ignored if GPIO9/RXT is
configured as an output.
0: Do not enable internal pull-down
1: Enable internal pull-down if configured as an input (will not be enabled if Pull up is enabled)
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Rev 1A