SC16C850V All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 5 — 19 January 2011 23 of 48
NXP Semiconductors
SC16C850V
Single UART with 128-byte FIFOs, IrDA, and XScale VLIO bus interface
[1] When RXINTLVL or TXINTLVL or FLWCNTH or FLWCNTL contains any value other than 0x00, receive and
transmit trigger levels are set by RXINTLVL, TXINTLVL; see Section 6.4 “
FIFO operation”.
7.4 Interrupt Status Register (ISR)
The SC16C850V provides six 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 provide the user with the highest pending
interrupt level to be serviced. No other interrupts are acknowledged until the pending
interrupt is serviced. A lower level interrupt may be seen after servicing the higher level
interrupt and re-reading the interrupt status bits. Table 12 “
Interrupt source” shows the
data values (bits 5:0) for the six prioritized interrupt levels and the interrupt sources
associated with each of these interrupt levels.
Table 11. TX FIFO trigger levels
FCR[5] FCR[4] TX FIFO trigger level in 32-byte FIFO mode
[1]
0 0 16 bytes
0 1 8 bytes
1 0 24 bytes
1 1 30 bytes
Table 12. Interrupt source
Priority
level
ISR[5] ISR[4] ISR[3] ISR[2] ISR[1] ISR[0] Source of the interrupt
1 000110LSR (Receiver Line Status Register)
2 000100RXRDY (Received Data Ready)
2 001100RXRDY (Receive Data time-out)
3 000010TXRDY (Transmitter Holding
Register Empty)
4 000000MSR (Modem Status Register)
5 010000RXRDY (Received Xoff signal)/
Special character
6 100000CTS, RTS change of state
Table 13. Interrupt Status Register bits description
Bit Symbol Description
7:6 ISR[7:6] FIFOs enabled. These bits are set to a logic 0 when the FIFOs are not being
used in the non-FIFO mode. They are set to a logic 1 when the FIFOs are
enabled in the SC16C850V mode.
logic 0 or cleared = default condition
5:4 ISR[5:4] INT priority bits 4:3. These bits are enabled when EFR[4] is set to a logic 1.
ISR[4] indicates that matching Xoff character(s) have been detected. ISR[5]
indicates that CTS, RTS have been generated. Note that once set to a
logic 1, the ISR[4] bit will stay a logic 1 until Xon character(s) are received.
logic 0 or cleared = default condition
3:1 ISR[3:1] INT priority bits 2:0. These bits indicate the source for a pending interrupt at
interrupt priority levels 1, 2, and 3 (see Table 12
).
logic 0 or cleared = default condition