XR21V1412_10 Datasheet, PDF (17/30 Pages) Exar Corporation – 2-CH FULL-SPEED USB UART

XR21V1412
REV. 1.1.0
2-CH FULL-SPEED USB UART
3.3 UART Register Descriptions
3.3.1 UART_ENABLE Register Description (Read/Write)
This register enables the UART TX and RX. For proper functionality, the UART TX and RX must be enabled in
the following order:
FIFO_ENABLE_CHx = 0x1 // Enable TX FIFO
UART_ENABLE = 0x3
// Enable TX and RX of that channel
FIFO_ENABLE_CHx = 0x3 // Enable RX FIFO
UART_ENABLE[0]: Enable UART TX
• Logic 0 = UART TX disabled.
• Logic 1 = UART TX enabled.
UART_ENABLE[1]: Enable UART RX
• Logic 0 = UART RX disabled.
• Logic 1 = UART RX enabled.
UART_ENABLE[7:2]: Reserved
These bits are reserved and should remain ’0’.
3.3.2 CLOCK_DIVISOR0, CLOCK_DIVISOR1, CLOCK_DIVISOR2 Register Description (Read/Write)
These registers are used for programming the baud rate. The V1412 uses a 19-bit divisor and 16-bit mask
register. Using the internal 48MHz oscillator, the 19-bit divisor is calculated as follows:
CLOCK_DIVISOR = Trunc ( 48000000 / Baud Rate )
For example, if the the baud rate is 115200bps, then
CLOCK_DIVISOR = Trunc ( 48000000 / 115200 ) = Trunc (416.66667) = 416
CLOCK_DIVISOR0[7:0]: Baud rate clock divisor bits [7:0]
CLOCK_DIVISOR1[7:0]: Baud rate clock divisor bits [15:8]
CLOCK_DIVISOR2[2:0]: Baud rate clock divisor bits [18:16]
CLOCK_DIVISOR2[7:3]: Reserved
These bits are reserved and should remain ’0’.
3.3.3 TX_CLOCK_MASK0, TX_CLOCK_MASK1 Register Description (Read/Write)
A look-up table is used for the value of the 16-bit TX Clock mask registers. The index of the look-up table is
calculated as follows:
index = Trunc ( ( ( 48000000 / Baud Rate ) - CLOCK_DIVISOR ) * 32)
For example, if the baud rate is 115200bps, then the index will be:
index = Trunc ( ( ( 48000000 / 115200 ) - 416 ) * 32) = Trunc (21.3333) = 21
The values for some baud rates to program the TX_CLOCK_MASK registers are listed in Table 8. For baud
rates that are not listed, use the index to select TX_CLOCK_MASK register values from Table 9.
3.3.4 RX_CLOCK_MASK0, RX_CLOCK_MASK1 Register Description (Read/Write)
The values for some baud rates to program the RX_CLOCK_MASK registers are listed in Table 8. For baud
rates that are not listed, use the same index calculated for the TX_CLOCK_MASK register to select
RX_CLOCK_MASK register values from Table 9.
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