XR17V254_08 Datasheet, PDF (42/70 Pages) Exar Corporation – 66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT

XR17V254
66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
REV. 1.0.1
IER[1]: TX Ready Interrupt Enable
In non-FIFO mode, a TX interrupt is issued whenever the THR is empty. In the FIFO mode, an interrupt is
issued twice: once when the number of bytes in the TX FIFO falls below the programmed trigger level and
again when the TX FIFO becomes empty. When autoRS485 mode is enabled (FCTR bit [5] = 1), the second
interrupt is delayed until the transmitter (both the TX FIFO and the TX Shift Register) is empty.
• Logic 0= Disable Transmit Ready Interrupt (default).
• Logic 1 = Enable Transmit Ready Interrupt.
IER[0]: RX Interrupt Enable
The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when
the receive FIFO has reached the programmed trigger level in the FIFO mode.
• Logic 0 = Disable the receive data ready interrupt (default).
• Logic 1 = Enable the receiver data ready interrupt.
5.5 Interrupt Status Register (ISR) - Read Only
The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The
Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the
ISR will give the user the current highest pending interrupt level to be serviced, others queue up for next
service. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt Source
Table, Table 15, shows the data values (bit [5:0]) for the six prioritized interrupt levels and the interrupt sources
associated with each of these interrupt levels.
5.5.1 Interrupt Generation:
• LSR is by any of the LSR bits [4:1]. See IER bit [2] description above.
• RXRDY is by RX trigger level.
• RXRDY Time-out is by a 4-char plus 12 bits delay timer.
• TXRDY is by TX trigger level or TX FIFO empty (or transmitter empty in auto RS-485 control).
• MSR is by any of the MSR bits [3:0].
• Receive Xon/Xoff/Special character is by detection of a Xon, Xoff or Special character.
• CTS#/DSR# is when the input pin toggles (from LOW to HIGH) during auto CTS/DSR flow control.
• RTS#/DTR# is when the output pin toggles (from LOW to HIGH) during auto RTS/DTR flow control.
• Wake-up Indicator is when the UART comes out of sleep mode.
5.5.2 Interrupt Clearing:
• LSR interrupt is cleared by a read to the LSR register.
• RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level.
• RXRDY Time-out interrupt is cleared by reading RHR.
• TXRDY interrupt is cleared by a read to the ISR register or writing to THR.
• MSR interrupt is cleared by a read to the MSR register.
• Xon or Xoff interrupt is cleared by a read to ISR register.
• Special character interrupt is cleared by a read to ISR or after the next character is received.
• RTS#/DTR# and CTS#/DSR# status change interrupts are cleared by a read to the MSR register.
• Wake-up indicator is cleared by a read to the INT0 register.
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