SC16C2550 Philips Semiconductors, SC16C2550 Datasheet - Page 21

• Manufacturer Part Number: SC16C2550
• Description: Dual UART with 16 bytes of transmit and receive FIFOs and infrared (IrDA) encoder/decoder
• Manufacturer: Philips Semiconductors

Philips Semiconductors
9397 750 11621
Product data
7.4 Interrupt Status Register (ISR)
Table 9:
Table 10:
The SC16C2550 provides four levels of prioritized interrupts to minimize external
software interaction. The Interrupt Status Register (ISR) provides the user with four
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.
“Interrupt source”
levels and the interrupt sources associated with each of these interrupt levels.
Table 11:
Bit
1
0
FCR[7]
0
0
1
1
Priority
level
1
2
2
3
4
5
6
ISR[5]
0
0
0
0
0
0
1
FIFO Control Register bits description
RCVR trigger levels
Interrupt source
Symbol
FCR[1]
FCR[0]
FCR[6]
0
1
0
1
Dual UART with 16 bytes of transmit and receive FIFOs and IrDA
shows the data values (bits 0-3) for the four prioritized interrupt
ISR[4]
0
0
0
0
0
1
0
Rev. 03 — 19 June 2003
Description
RCVR FIFO reset.
FIFOs enabled.
Logic 0 = Receive FIFO not reset (normal default condition).
Logic 1 = Clears the contents of the receive FIFO and resets the
FIFO counter logic (the receive shift register is not cleared or
altered). This bit will return to a logic 0 after clearing the FIFO.
Logic 0 = Disable the transmit and receive FIFO (normal default
condition).
Logic 1 = Enable the transmit and receive FIFO. This bit must
be a ‘1’ when other FCR bits are written to, or they will not
be programmed.
ISR[3]
0
0
1
0
0
0
0
RX FIFO trigger level
01
04
08
14
ISR[2]
1
1
1
0
0
0
0
ISR[1]
1
0
0
1
0
0
0
…continued
ISR[0]
0
0
0
0
0
0
0
© Koninklijke Philips Electronics N.V. 2003. All rights reserved.
Source of the interrupt
LSR (Receiver Line Status
Register)
RXRDY (Received Data
Ready)
RXRDY (Receive Data
time-out)
TXRDY (Transmitter
Holding Register Empty)
MSR (Modem Status
Register)
RXRDY (Received Xoff
signal) / Special character
CTS, RTS change of state
SC16C2550
encoder/decoder
Table 11
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