XR21V1414 Datasheet, PDF (10/26 Pages) Exar Corporation – 4-CH FULL-SPEED USB UART

XR21V1414
4-CH FULL-SPEED USB UART
REV. 1.0.0
1.4.1.1 9-Bit Data Mode
In 9-bit data mode, 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.
1.4.2 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.
1.4.2.1 Character Mode
In character mode, up to 64 bytes of data can be sent at a time to the USB host.
1.4.2.2 Character + Status Mode
In this mode, each 8-bit character and the 4 error bits associated with it can be transmitted to the USB host.
The 4 error bits will be in the second byte following the 8-bit character. In this mode, up to 32 character bytes
are sent per bulk-in packet.
1.4.2.3 9-Bit Data Mode
In 9-bit data mode, two bytes of data are sent to the USB host for each byte 9-bit data that is received. The first
byte sent to the USB host is the first 8-bits of data. Bit-0 of the second byte is the bit-9 of the data.
1.4.3 GPIO
Each UART has 6 GPIOs. By default, the GPIOs are general purpose I/Os. However, there are few modes
that can be enabled to add additional feature such as Auto RTS/CTS Flow control, Auto DTR/DSR Flow
Control or Transceiver Enable Control. See Table 13.
1.4.4 Automatic RTS/CTS Hardware Flow Control
GPIO5 and GPIO4 of the UART channel can be enabled as the RTS# and CTS# signals for Auto RTS/CTS
flow control when GPIO_MODE[2:0] = ’001’ and FLOW_CONTROL[2:0] = ’001’. Automatic RTS flow control is
used to prevent data overrun errors in local RX FIFO by de-asserting the RTS signal to the remote UART.
When there is room in the RX FIFO, the RTS pin will be re-asserted. Automatic CTS flow control is used to
prevent data overrun to the remote RX FIFO. The CTS# input is monitored to suspend/restart the local
transmitter (see Figure 3):
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