XR21B1424_17 Datasheet, PDF (5/64 Pages) Exar Corporation – Enhanced 4-Ch Full-Speed USB UART

XR21B1424
Pin Assignments
Pin No.
Pin Name
1
RXA
2
GPIOA5/RTSA#/RS485A
3
GPIOA4/CTSA#
4
GPIOA3/DTRA#
5
GPIOA2/DSRA#
6
GPIOA1/CDA#
7
GPIOA0/RIA#/RWKA#
8
GND
9
USBD+
10
USBD-
11
VIO
12
VCC
13
VCC_REG
14
NC
15
NC
16
VBUS_SENSE
17
RESET#
Type
I
I/O
I/O
I/O
I/O
I/O
I/O
PWR
I/O
I/O
PWR
PWR
PWR
-
-
I
I/O / OD
Description
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.
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.
Power supply common, ground.
USB port differential data positive. This pin has internal pull-up resistor compliant to the USB
2.0 specification. The ESD protection on this pin is ±15kV HBM.
USB port differential data negative. The ESD protection on this pin is ±15kV HBM.
I/O voltage input to the UART/GPIO pins. Must be between 1.8 and 3.6V. May be connected to
VCC (pin 12) if VCC_REG input voltage is 5V. See “USB Power Modes” on page 12.
3.3V power to the device, or 3.3V power output from the device when 5V power is supplied to
VCC_REG pin. 3.3V output power can source up to 200 mA maximum (including the device)
and should be decoupled by minimum of 4.7μF ceramic capacitor. See “USB Power Modes”
on page 12.
5V or 3.3V power to the device. In bus-powered mode, connect VBUS power from the USB
host to this pin and to the VBUS_SENSE pin - see Figure 1. To conform to USB specifications,
an inrush current limiting circuit is recommended. In self-powered mode, connect on-board 5V
or 3.3V source to this pin and VBUS from the USB host to the VBUS_SENSE pin. See
Figure 2 and Figure 3. USB specification requires a minimum of 1uF and a maximum of 10uF
of decoupling on VBUS power.
No Connect.
No Connect.
Must be connected to VBUS power from the USB host PC. This pin is used to disable the inter-
nal pull-up resistor on the USBD+ signal when VBUS is not present. In bus-powered mode,
connect VBUS (5V) power from the USB host to this pin and to the VCC_REG pin - see Figure
1. In self-powered mode, connect VBUS from the USB host to this pin. This pin must be
decoupled by a 4.7 uF tantalum capacitor.
Active low open drain output. Asserted at power on or any time device is reset by either regis-
ter or USB bus reset. As an input, must be asserted for at least 15μs to force a device reset.
Reset pulse width input of shorter than 15μs will have unknown effects. A weak internal pull-up
resistor provides noise immunity if left unconnected.
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