XR21V1410IL-0A-EB Datasheet, PDF (7/28 Pages) Exar Corporation – 1-CH FULL-SPEED USB UART

XR21V1410
REV. 1.3.0
1-CH FULL-SPEED USB UART
• Bit 6 is Self-powered mode - set to ’0’ for bus-powered, set to ’1’ for self-powered
• Bit 5 is Remote Wakeup support - set to ’0’ for no support, set to ’1’ for remote wakeup support
• Bit 4:0 are reserved - set to ’0’
1.3.1.4 Device Maximum Power
The Device Maximum Power value replaces the bMaxPower field in the USB Standard Configuration
Descriptor. The value specified is in units of 2 mA. For example, the value 0x2F is decimal 47 or 94 mA. Note
that the default bMaxPower of the V1410 device is 94 mA.
1.4 UART Manager
The UART Manager enables/disables the UART including the TX and RX FIFOs. The UART Manager is
located in a separate register block from the UART registers.
1.5 UART
The UART can be configured via USB control transfers from the USB host. The UART transmitter and receiver
sections are described seperately in the following sections. At power-up, the V1410 will default to 9600 bps, 8
data bits, no parity bit, 1 stop bit, and no flow control. If a standard CDC driver accesses the V1410, defaults
will change. See ”Section 1.2, USB Device Driver” on page 5.
1.5.1 Transmitter
The transmitter consists of a 128-byte TX FIFO and a Transmit Shift Register (TSR). Once a bulk-out packet
has been received and the CRC has been validated, the data bytes in that packet are written into the TX FIFO
of the specified UART channel. Data from the TX FIFO is transferred to the TSR when the TSR is idle or has
completed sending the previous data byte. The TSR shifts the data out onto the TX output pin at the data rate
defined by the CLOCK_DIVISOR and TX_CLOCK_MASK registers. The transmitter sends the start bit
followed by the data bits (starting with the LSB), inserts the proper parity-bit if enabled, and adds the stop-
bit(s). The transmitter can be configured for 7 or 8 data bits with or without parity or 9 data bits without parity.
If 9 bit data is selected without wide mode, the 9th bit will always be ’0’.
1.5.1.1 Wide Mode Transmit
When both 9 bit data and wide mode are enabled, two bytes of data must be written. The first byte that is
loaded into the TX FIFO are the first 8 bits (data bits 7-0) of the 9-bit data. Bit-0 of the second byte that is
loaded into the TX FIFO is bit-8 of the 9-bit data. The data that is transmitted on the TX pin is as follows: start
bit, 9-bit data, stop bit. Use the WIDE_MODE register to enable wide mode.
1.5.2 Receiver
The receiver consists of a 384-byte RX FIFO and a Receive Shift Register (RSR). Data that is received in the
RSR via the RX pin is transferred into the RX FIFO along with any error tags such as Framing, Parity, Break
and Overrun errors. Data from the RX FIFO can be sent to the USB host by sending a bulk-in packet.
If the wide mode is not enabled, then 7 or 8 bits of data and optionally a parity bit are transferred to the USB
host.
1.5.2.1 Wide mode Receive
In wide mode, the V1410 receives a 7, 8 or 9 bit character and then forwards the character along with 3
associated error bits to the USB host in two bytes. If data is 7 or 8 bits, a parity bit is also received and checked
if enabled. If data is 9 bits, no parity is checked. The 9th bit of data is in bit position 0 along with the 3 error bits,
break, frame error and overrun error flags in bit positions 1, 2 & 3 respectively. In wide mode, the parity and
framing error and break flag are associated with the character that they accompany and the overrun error is
tied to the current contents of the entire RX FIFO.
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