XR21B1424_17 Datasheet, PDF (6/64 Pages) Exar Corporation – Enhanced 4-Ch Full-Speed USB UART

XR21B1424
Pin No.
Pin Name
18
USB_STAT2
19
GPIOC9/RXTC
20
GPIOC8/TXTC
21
NC
22
GPIOC7/RS485C
23
GPIOC6/CLKC
24
TXC
25
USB_STAT1
26
RXC
27
GPIOC5/RTSC#/RS485C
28
GPIOC4/CTSC#
29
GPIOC3/DTRC#
30
GPIOC2/DSRC#
31
GPIOC1/CDC#
32
TEST#
33
GPIOC0/RIC#/RWKC#
34
GPIOB9/RXTB
Type
O / OD
I/O
I/O
-
I/O
I/O
O
O
I
I/O
I/O
I/O
I/O
I/O
I
I/O
I/O
Description
This pin has the same functionality as the USB_STAT1 pin. However, the default output for this
pin is active low polarity, asserted whenever the XR21B1424 is placed into a suspended state.
This default may be changed via the PIN_CFG_USB_STAT2 register.
General purpose I/O, or UART receive data indicator. Defaults to GPIO input with internal pull-
up resistor. See “TXT and RXT Pins” on page 19. When configured as receive indicator, this
pin will toggle at ~10Hz intervals while the UART is receiving data.
General purpose I/O, or UART transmit data indicator. Defaults to GPIO input with internal pull-
up resistor. See “TXT and RXT Pins” on page 19. When configured as transmit indicator, this
pin will toggle at ~10Hz intervals while the UART is transmitting data.
No Connect.
General purpose I/O, or RS-485 half-duplex enable output. Defaults to GPIO input with internal
pull-up resistor.
General purpose I/O, or clock or pulse output. Defaults to GPIO input with internal pull-up
resistor. See “Programmable Output Clock” on page 16.
UART Transmit Data.
The USB_STAT1 output pin may be used to indicate any of three USB status conditions:
1. USB_STAT1 is asserted when the USB host asserts USB reset.
2. USB_STAT1 is asserted when the USB host PC places the XR21B1424 device into the sus-
pended state.
3. USB_STAT1 is asserted when it is not safe to draw the amount of current requested in the
Device Maximum Power field of the Configuration Descriptor.
a. For a low power device (<=1 unit load or 100mA, bMaxPower <= 0x32), USB_STAT1 will be
asserted when the USB UART is in the suspended state.
b. For a high power device (bMaxPower > 0x32), USB_STAT1 will be asserted when the USB
UART is in the suspended state or when it is not yet configured.
The assertion polarity and status condition are selectable via the PIN_CFG_STAT1 register.
The USB_STAT pin will be de-asserted whenever the selected condition(s) is/are not met. The
default output for this pin is active high polarity, asserted whenever the XR21B1424 is placed
into a suspended state.
UART Receive Data.
General purpose I/O, or UART Request-to-Send output (active low), or auto RS-485 half-
duplex control. Defaults to GPIO input with internal pull-up resistor. See “Automatic RTS/CTS
Hardware Flow Control” on page 16 or “Multidrop mode with address matching” on page 18.
General purpose I/O, or UART Clear-to-Send input (active low). Defaults to GPIO input with
internal pull-up resistor. See “Automatic RTS/CTS Hardware Flow Control” on page 16.
General purpose I/O, or UART Data-Terminal-Ready push-pull output (active low). Defaults to
GPIO input with internal pull-up resistor. See “Automatic DTR/DSR Hardware Flow Control” on
page 17.
General purpose I/O, or UART Data-Set-Ready input (active low). Defaults to GPIO input with
internal pull-up resistor. See “Automatic DTR/DSR Hardware Flow Control” on page 17.
General purpose I/O, or UART Carrier-Detect input (active low). Defaults to GPIO input with
internal pull-up resistor.
Test mode. Must be left open or pulled high to VIO for normal operation.
General purpose I/O, or UART Ring-Indicator input (active low), or Remote Wakeup input.
Defaults to GPIO input with internal pull-up resistor. Wakeup signaling to the USB host is sent
when a falling edge is detected. See “Remote Wakeup” on page 10.
General purpose I/O, or UART receive data indicator. Defaults to GPIO input with internal pull-
up resistor. See “TXT and RXT Pins” on page 19. When configured as receive indicator, this
pin will toggle at ~10Hz intervals while the UART is receiving data.
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exar.com/XR21B1424
Rev 1C