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PDF XR21B1424 Data sheet ( Hoja de datos )
| Número de pieza | XR21B1424 | |
| Descripción | Enhanced 4-Ch Full-Speed USB UART | |
| Fabricantes | Exar | |
| Logotipo |  |
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XR21B1424
Enhanced 4-Ch Full-Speed USB UART
General Description
The XR21B1424 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 XR21B1424 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 XR21B1424 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 XR21B1424 operates from a single 5V or 3.3V power supply. When
powered with 5V input, a regulated 3.3V output is supplied.
Typical Application
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
• 64-pin LQFP 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 61
XR21B1424
MCU
USB UART
© 2014 Exar Corporation
1 / 61
exar.com/XR21B1424
Rev 1B
1 page  
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#
18 USB_STAT2
19 GPIOC9/RXTC
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
O / OD
I/O
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. 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. 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.
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.
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.
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.
© 2014 Exar Corporation
5 / 61
exar.com/XR21B1424
Rev 1B
5 Page 
XR21B1424
Table 1: USB String Descriptor Defaults
Descriptor
Exar USB Vendor ID
Exar USB Product ID
Manufacturer String
Product String
Value
0x04E2
0x1424
Exar Corp.
Exar USB UART
Device Driver
The XR21B1424 device may be used with either a standard CDC-ACM driver or an Exar supplied custom driver. The CDC-
ACM driver is native to the Operating System. In Linux, the CDC-ACM driver will automatically load for the XR21B1424, but
in the Windows OS, an extra INF file is required to install the CDC-ACM driver. The custom drivers must also be installed,
although for Windows 7 OS and newer with Internet access and Windows updates set to automatic, the latest Windows-
Certified (WHQL/HCK) driver will be downloaded and installed automatically.
CDC-ACM Driver
Because the CDC-ACM driver has no ability to access the XR21B1424 internal device registers, the device is initialized to
certain hardware defaults. By default the XR21B1424 enables hardware RTS/CTS flow control, GPIO7 is set as active high
auto RS-485 half-duplex control, and RI, CD and DSR pins are enabled to be interrupt sensitive. These settings are listed in
Table 2. Additionally, the low latency threshold in CDC mode is automatically set to 40,960 bps. Refer to “RX FIFO Low
Latency” on page 15. This threshold may be modified in the OTP CDC_ACM_BAUD_THRESH locations.
Table 2: XR21B1424 Register Defaults with CDC-ACM Driver
Register
FLOW_CONTROL
GPIO_MODE
GPIO_DIRECTION
GPIO_INT_MASK
Value
0x0001
0x0339
0x0028
0x03F0
Notes
Hardware flow control
RTS / CTS flow control, GPIO7 is used as RS-485 half-duplex enable (RS485)
with active high polarity. GPIO6 is a GPIO input, RXT and TXT remain enabled.
DTR / RTS are configured as outputs (TXT, RXT, CLK and RS485 are also spe-
cial function outputs). All other GPIOs are configured as inputs.
RI, CD and DSR are interrupt sensitive, i.e. can cause a USB interrupt to be
generated.
Custom Exar Driver
Custom Windows and Linux drivers are available from Exar. The custom driver allows software applications to make full use
of the XR21B1424 register set and features.
Note that a custom driver must always immediately set CUSTOM_DRIVER bit-0 = 1. Once CUSTOM_DRIVER bit-0 is set,
the custom driver can use standard CDC-ACM commands without the XR21B1424 automatically changing to the settings in
the Table 2.
© 2014 Exar Corporation
11 / 61
exar.com/XR21B1424
Rev 1B
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet XR21B1424.PDF ] | |
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