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PDF XR21B1421 Data sheet ( Hoja de datos )

Número de pieza XR21B1421
Descripción Enhanced 1-Ch Full-Speed USB HID to UART Bridge
Fabricantes Exar 
Logotipo Exar Logotipo



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General Description
The XR21B1421 is an enhanced Universal Asynchronous Receiver and
Transmitter (UART) bridge to HID class USB interface. The USB interface
is fully compliant to the USB 2.0 (Full-Speed) specification with 12 Mbps
USB data transfer rate. The USB interface also supports USB suspend,
resume and remote wakeup operations. The USB Vendor ID, Product ID,
power mode, remote wakeup support, maximum power, and numerous
other settings may be programmed in the no-chip OTP memory via the
USB interface using either HID reports or Exar-supplied OTP program-
ming tools.
The XR21B1421 includes an internal oscillator and does not require an
external crystal/oscillator. Any UART baud rate up to 12 Mbps may be
generated with this internal clock and the fractional baud rate generator.
The UART pins for each port may also be configured as GPIO; direction,
state, output driver type and input pull-up or pull-down resistors are pro-
grammed either through on chip OTP, or on the fly via memory mapped
registers.
Large 512-byte TX and RX FIFOs prevent buffer overflow errors and opti-
mize data throughput. Automatic half-duplex direction control and optional
multi drop (9-bit) mode simplify both hardware and software in half-duplex
RS-485 applications.
The XR21B1421 uses the native OS HID driver using HID reports. The
HID reports perform a variety of functions, including device configuration,
transmitting and receiving UART data, and programming of the on-chip
OTP. Exar provides a .dll as an easy to use programming interface to the
HID reports.
The XR21B1421 operates from a single 5V or 3.3V power supply and is
available in a 24 or 28 pin QFN package. When powered with 5V input,
the XR21B1421 supplies a regulated 3.3V output. The 24 pin package
has a separate VIO supply voltage input for the Modem / GPIO pins. The
28 pin package has VIO internally tied to 3.3V.
Block Diagram
USB
Internal
Oscillator
(48MHz)
USB Slave Interface
USB
Descriptors
OTP
Fractional
BRG
512-byte
TX FIFO
512-byte
RX FIFO
Internal
Status and
Control
Registers
GPIOs/
Modem IO
UART
LDO
3V3
XR21B1421
Enhanced 1-Ch Full-Speed
USB HID to UART Bridge
FEATURES
• ±15kV ESD on USBD+/USBD-
• USB 2.0 Compliant, Full-Speed (12Mbps)
• Unique pre-programmed USB serial number
• Internally generated 48MHz core clock
• Enhanced UART features
• Baud rates up to 12 Mbps
• Fractional Baud Rate Generator
• 512-byte TX and 512-byte RX FIFOs
• Auto Hardware / Software Flow Control
• Multidrop and Half-Duplex Modes
• Auto RS-485 Half-Duplex Control
• Selectable GPIO or Modem I/O
• Up to 10 GPIOs
• 5V tolerant GPIO inputs
• Suspend state GPIO configuration
• Configurable clock output
• 24-pin or 28-pin QFN package
• Industrial -40°C to +85°C Temperature Range
APPLICATIONS
• Portable Medical Diagnostics
• Blood Glucose Meters
• Health and Fitness Wellness Monitors
• Uninterruptible Power Supplies
• Energy Management Consoles
Ordering Information – page 50
TX
RX
© 2014 Exar Corporation
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exar.com/XR21B1421
Rev 1B

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XR21B1421 pdf
Pin Assignments
Pin No.
Pin Name
1 GPIO0/CLK
2 GND
3 USBD+
4 USBD-
5 VIO
6 VCC
7 VCC_REG
8 VBUS_SENSE
9 RESET#
10 NC
11 USB_STAT1
12 GPIO9/DSR#
13 GPIO8/DTR#
14 GPIO7/RI#/RWK#
XR21B1421
24-pin QFN
Type
I/O
PWR
I/O
I/O
PWR
PWR
PWR
I
I/O OD
OD
I/O
I/O
I/O
Description
General purpose I/O, or clock or pulse output. Defaults to GPIO input with internal pull-up. See
“GET / SET_GPIO_CONFIG” on page 28 and “GET / SET_PIN_CONFIG” on page 41.
Power supply common, ground.
USB port differential data positive input. This pin has internal pull-up resistor compliant to USB
2.0 specification. The ESD protection on this pin is +/-15 kV HBM.
USB port differential data negative input. The ESD protection on this pin is +/-15 kV HBM.
Supply voltage for the UART and GPIO signals. The voltage range for VIO is + 1.8V to + 3.6V. In
QFN28 package, the VIO is internally tied to core 3.3V. If VCC_REG is powered by 5V, VCC out-
put 3.3V may be externally connected to VIO pin.
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 may source up to 200 mA maximum (including the device) and
should be decoupled by minimum of 4.7 uF ceramic capacitor.
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. 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.
Must be connected to VBUS power from the USB host PC. This pin is used to disable the internal
pull-up resistor on the USBD+ signal when VBUS is not present in self-powered mode.
Active low open drain output. Asserted at power on or any time device is reset by either register
or USB bus reset. As an input, must be asserted for at least 15 us to force a device reset. Reset
pulse width input of shorter than 15 us will have unknown effects. A weak internal pull-up resistor
provides noise immunity if left unconnected.
No Connect
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 XR21B1421 device into the sus-
pend 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 100 mA, bMaxPower <= 0x32), USB_STAT1 will be
asserted when the USB UART is in the suspend mode.
b. For a high power device (bMaxPower > 0x32), USB_STAT1 will be asserted when the USB
UART is in the suspend mode 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 XR21B1421 is placed into
a suspended state.
General purpose I/O, or UART Data-Set-Ready input (active low). Defaults to GPIO push-pull
output. See “Automatic DTR/DSR Hardware Flow Control” on page 16.
General purpose I/O, or UART Data-Terminal-Ready push-pull output (active low). Defaults to
GPIO push-pull output. See “Automatic DTR/DSR Hardware Flow Control” on page 16.
General purpose I/O, or UART Ring-Indicator input (active low) or Remote Wakeup input (active
low). Defaults to GPIO input with internal pull-up.
© 2014 Exar Corporation
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exar.com/XR21B1421
Rev 1B

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XR21B1421 arduino
XR21B1421
Table 1: USB String Descriptor Defaults
Descriptor
Exar USB Vendor ID
Exar USB Product ID
Manufacturer String
Product String
Value
0x04E2
0x1421
Exar Corp.
Exar USB UART
Device Driver
The XR21B1421 device will utilize the native OS supplied HID driver. No other driver is required, however a custom dll sup-
plied by Exar provides a function library to any user that is developing applications that utilize the HID reporting capabilities.
Exar also supplies a sample GUI using the .dll as well as source code (upon request).
USB Power Modes
The XR21B1421 device may be configured in any one of three power modes: Bus-powered, Self-powered 5V, or Self-pow-
ered 3.3V. In all three modes, the VBUS power signal from the USB host must be connected to the VBUS_SENSE pin of
the device.
The default power mode for the XR21B1421 is bus-powered. In this mode, a maximum power required for the USB device
from the host must be specified. In this context, the USB device includes all components on the PCB that will draw power
from the USB VBUS power. The default power request for the XR21B1421 is 100 mA but this may be changed using the
Maxpower field of the SET_USB_CONFIG HID report.
Bus-Powered
In bus-powered mode, VBUS from the USB cable supplies 5V to the XR21B1421 device. The VCC pin will supply 3.3V out-
put. The VIO pins may be externally connected to VCC or to an alternate voltage source.
VBUS
Dp
Dm
GND
USB Connector
XR21B1421
VCC_REG
VBUS_SENSE
Dp
Dm
GND
VCC
VIO
Figure 1: Bus-Powered Mode
© 2014 Exar Corporation
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exar.com/XR21B1421
Rev 1B

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