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PDF XR21B1422 Data sheet ( Hoja de datos )
| Número de pieza | XR21B1422 | |
| Descripción | Enhanced 2-Ch Full-Speed USB UART | |
| Fabricantes | Exar | |
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XR21B1422
Enhanced 2-Ch Full-Speed USB UART
General Description
The XR21B1422 is an enhanced Universal Asynchronous Receiver and
Transmitter (UART) bridge to 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 on-chip OTP memory via the
USB interface.
The XR21B1422 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 XR21B1422 uses the native OS CDC-ACM driver or an Exar supplied
custom driver. Exar provides WHQL/HCK-certified software drivers for
Windows 2000, XP, Vista, 7, 8, 8.1 as well as software drivers for Windows
CE, Linux and Mac OS X. Full source code is available.
The XR21B1422 operates from a single 5V or 3.3V power supply. When
powered with 5V input, a regulated 3.3V output is supplied.
Block Diagram
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 per channel
• 5V tolerant GPIO inputs
• Suspend state GPIO configuration
• Configurable clock output
• 40-pin QFN package
• Industrial -40°C to +85°C Temperature Range
APPLICATIONS
• Building Automation
• Security Systems
• Factory and Process Control
• ATM Terminals
• USB to Serial Controllers
Ordering Information – page 60
Internal
Oscillator
(48MHz)
USB
USB Slave Interface
USB
Descriptors
OTP
Fractional
BRG
512-byte
TX FIFO
512-byte
RX FIFO
Internal
Status and
Control
Registers
GPIOs/
Modem IO
VIO
TX
RX
LDO
UART Ch A
3V3 UART Ch B
(same as Ch A)
1840k
1610k
1380k
1150k
920k
690k
460k
230k
0k
Throughput Comparison
Competitor
Exar
230k
460k
920k
Data Rate (bps)
1840k
© 2014 Exar Corporation
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exar.com/XR21B1422
Rev 1A
1 page  
Pin Assignments
Pin No.
Pin Name
1 GPIOA8/TXTA
2 GPIOA9/RXTA
3 NC
4 NC
5 GND
6 USBD+
7 USBD-
8 VIO
9 VCC
10 VCC_REG
11 VBUS_SENSE
12 RESET#
13 NC
14 USB_STAT2
15 USB_STAT1
XR21B1422
Type
I/O
I/O
-
-
PWR
I/O
I/O
PWR
PWR
PWR
I
I/O OD
-
O / OD
O
Description
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 18. When configured as transmit indicator, this
pin will toggle at ~10Hz intervals while the UART is transmitting data.
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 18. When configured as receive indicator, this
pin will toggle at ~10Hz intervals while the UART is receiving data.
No Connect.
No Connect.
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 11.
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 11.
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 inter-
nal pull-up resistor on the USBD+ signal when VBUS is not present.
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.
No Connect.
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 XR21B1422 is placed into a suspended state.
This default may be changed via the PIN_CFG_USB_STAT2 register.
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 XR21B1422 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 100mA, bMaxPower <= 0x32), USB_STAT1 will be
asserted when the USB UART is in the suspend mode or when it is not yet configured.
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 XR21B1422 is placed
into a suspended state.
© 2014 Exar Corporation
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Rev 1A
5 Page 
XR21B1422
USB Power Modes
The XR21B1422 device may be configured in any of the following power modes: bus-powered, self-powered 5V, or self-
powered 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 XR21B1422 is bus powered. In this mode, the USB device’s maximum power requirement
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 host VBUS power. The default maximum power for the XR21B1422 is 100mA. This may be changed using
the Attributes field in the OTP.
Bus-Powered
In bus-powered mode, VBUS from the USB cable supplies 5V to the XR21B1422 device. The VCC pin will supply a 3.3V
output. The VIO pins may be externally connected to VCC or to an alternate voltage source.
VBUS
Dp
Dm
GND
USB Connector
XR21B1422
VCC_REG
VBUS_SENSE
Dp
Dm
GND
VCC
VIO
Figure 1: Bus-Powered Mode
Self-Powered 5V
In self-powered 5V mode, a local source provides 5V to the XR21B1422 device. The USB attributes should be changed in
the OTP to correctly report self-powered mode. The VCC pin will supply a 3.3V output. VIO pins may be externally con-
nected to VCC or to an alternate voltage source.
5V
Supply
VBUS
Dp
Dm
GND
USB Connector
XR21B1422
VCC_REG
VBUS_SENSE
Dp
Dm
GND
VCC
VIO
Figure 2: Self-Powered 5V Mode
© 2014 Exar Corporation
11 / 60
exar.com/XR21B1422
Rev 1A
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet XR21B1422.PDF ] | |
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