XR19L200 Datasheet, PDF (19/40 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

PRELIMINARY
XR19L200
REV. P1.0.2
SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
4.5 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 are queued up to be
serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt
Source Table, Table 7, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources
associated with each of these interrupt levels.
4.5.1 Interrupt Generation:
• LSR is by any of the LSR bits 1, 2, 3 and 4.
• 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.
• MSR is by any of the MSR bits 0, 1, 2 and 3.
• Receive Xoff/Special character is by detection of a Xoff or Special character.
• Wake-up Interrupt is when the device wakes up from sleep mode. See Sleep Mode section for more details.
4.5.2 Interrupt Clearing:
• LSR interrupt is cleared by reading the LSR register (but FIFO error bit does not clear until the character(s)
that generated the interrupt(s) is (are) read from the FIFO).
• RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level.
• RXRDY Time-out interrupt is cleared by reading the RHR register.
• TXRDY interrupt is cleared by reading the ISR register or writing to the THR register.
• MSR interrupt is cleared by reading the MSR register.
• Xoff interrupt is cleared by reading the ISR or when Xon character(s) is received.
• Special character interrupt is cleared by reading the ISR or after the next character is received.
• Wake-up interrupt is cleared by reading the ISR register.
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TABLE 7: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY
ISR REGISTER STATUS BITS
SOURCE OF INTERRUPT
LEVEL BIT-5 BIT-4 BIT-3 BIT-2 BIT-1
BIT-0
1
0
0
0
1
1
0 LSR (Receiver Line Status Register)
2
0
0
1
1
0
0 RXRDY (Receive Data Time-out)
3
0
0
0
1
0
0 RXRDY (Received Data Ready)
4
0
0
0
0
1
0 TXRDY (Transmit Ready)
5
0
0
0
0
0
0 MSR (Modem Status Register)
6
0
1
0
0
0
0 RXRDY (Received Xoff or Special character)
-
0
0
0
0
0
1 None (default) or Wake-up Interrupt
ISR[0]: Interrupt Status
• Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
• Logic 1 = No interrupt pending (default condition) or wake-up interrupt. The wake-up interrupt is issued when
the L200 has been awakened from sleep mode.
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