XR21V1412IL-0A Datasheet, PDF (7/32 Pages) Exar Corporation – 2-CH FULL-SPEED USB UART

XR21V1412
REV. 1.3.0
2-CH FULL-SPEED USB UART
1.0 FUNCTIONAL DESCRIPTIONS
1.1 USB interface
The USB interface of the V1412 is compliant with the USB 2.0 Full-Speed Specifications. The USB
configuration model presented by the V1412 to the device driver is compatible to the Abstract Control Model of
the USB Communication Device Class (CDC-ACM). The V1412 uses the following set of parameters:
• 1 Control Endpoint
■ Endpoint 0 as outlined in the USB specifications
• 1 Configuration is supported
• 2 interfaces per UART channel
■ Each UART channel has a single interrupt endpoint
■ Each UART channel have bulk-in and bulk-out endpoints
1.1.1 USB Vendor ID
Exar’s USB Vendor ID is 0x04E2. This is the default Vendor ID that is used for the V1412 unless a valid
EEPROM is present on the I2C interface signals. If a valid EEPROM is present, the Vendor ID from the
EEPROM will be used.
1.1.2 USB Product ID
The default USB Product ID for the V1412 is 0x1412. If a valid EEPROM is present, the Product ID from the
EEPROM will be used. Note that Exar’s custom drivers for all Windows OS require that the Product ID be an
even number for the V1412 device for proper identification of the device.
1.2 USB Device Driver
The V1412 device can be used with either a standard CDC-ACM driver or a custom driver. When the CDC-
ACM driver is used, the driver has no capability to read or write the V1412 device registers. Because of this,
the V1412 device is initialized to the settings in Table 1: With a custom driver, all GPIOs default in hardware to
inputs but these settings may be modified by the custom driver.
TABLE 1: V1412 REGISTER DEFAULTS WITH CDC-ACM DRIVER
REGISTER
VALUE
NOTES
FLOW_CONTROL
0x01
Hardware flow control
GPIO_MODE
0x01
RTS / CTS flow control
GPIO_DIRECTION
0x08
GPIO3/DTR# configured as an output
GPIO_INT_MASK
0x30
GPIO0/RI#, GPIO1/CD# and GPIO2/DSR# are interrupt sensi-
tive, i.e. can cause a USB interrupt to be generated
Note that when using a CDC-ACM driver, the V1412 will automatically change the bMaxPacketSize to 63 bytes
to compensate for a known issue with the Microsoft CDC-ACM device driver. A register is available to change
this setting with a custom driver as well. See “Section 3.4.1, CUSTOM Register Description - Chan A / B
(Read/Write)” on page 25. Although there is no ability to read / write registers when using the CDC-ACM
driver, basic UART functions, including setting baud rate, character format and sending line break are
supported by the CDC driver. Refer to the 4 CDC_ACM_IF USB Control Commands listed in Table 4,
“Supported USB Control Commands,” on page 14.
1.3 I²C Interface
The I²C interface provides connectivity to an external I²C memory device (i.e. EEPROM) that can be read by
the V1412 for configuration. If no external EEPROM is present, the SDA and SCL are used to specify remote
wakeup support and power mode as described in Table 2. These pins are sampled at power-up.
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