Rainbow Electronics W90N740 - Manual (Page 158)

W90N740
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7.9 UART Controller
The Universal Asynchronous Receiver/Transmitter (UART) performs a serial-to-parallel conversion
on data characters received from the peripheral such as MODEM, and a parallel-to-serial conversion on
data characters received from the CPU.
There are five types of interrupts, i.e., line status interrupt, transmitter FIFO empty interrupt, receiver
threshold level reaching interrupt, time out interrupt, and MODEM status interrupt. One 16-byte
transmitter FIFO (TX_FIFO) and one 16-byte (plus 3-bit of error data per byte) receiver FIFO (RX_FIFO)
has been built in to reduce the number of interrupts presented to the CPU. The CPU can completely read
the status of the UART at any time during the operation. The reported status information includes the
type and condition of the transfer operations being performed by the UART, as well as any error
conditions (parity, overrun, framing, or break interrupt) found. The UART includes a programmable baud
rate generator that is capable of dividing crystal clock input by divisors to produce the clock that
transmitter and receiver needed. The equation is
BaudOut = crystal clock / 16 * [Divisor + 2].
The Features of the UART:
• Transmitter and receiver are buffered with a 16-byte FIFO each to reduce the number of
interrupts.
• Full set of MODEM control functions (CTS, RTS, DSR, DTR, RI and DCD)
• Fully programmable serial-interface characteristics:
-- 5-, 6-, 7-, or 8-bit character
-- Even, odd, or no-parity bit generation and detection
-- 1-, 1&1/2, or 2-stop bit generation
-- Baud rate generation
• Break generation and detection
• False start bit detection
• Parity, overrun, and framing error detection
• Full prioritized interrupt system controls