sc68c652b NXP Semiconductors, sc68c652b Datasheet - Page 20

• Manufacturer Part Number: sc68c652b
• Description: Sc68c652b 5 V, 3.3 V And 2.5 V Dual Uart, 5 Mbit/s Max. With 32-byte Fifos, Irda Encoder/decoder, And Motorola Up Interface
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 14657
Product data sheet
7.4 Interrupt Status Register (ISR)
The SC68C652B 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.
data values (bit 0 to bit 5) for the six prioritized interrupt levels and the interrupt sources
associated with each of these interrupt levels.
Table 14:
Table 15:
Priority
level
1
2
2
3
4
5
6
Bit
7:6
5:4
3:1
0
ISR[5] ISR[4] ISR[3] ISR[2] ISR[1] ISR[0] Source of the interrupt
0
0
0
0
0
0
1
Interrupt source
Interrupt Status Register bits description
Symbol
ISR[7:6]
ISR[5:4]
ISR[3:1]
ISR[0]
0
0
0
0
0
1
0
Rev. 01 — 25 April 2005
Description
FIFOs enabled. These bits are set to a logic 0 when the FIFOs are not
being used in the 16C450 mode. They are set to a logic 1 when the
FIFOs are enabled in the SC68C652B mode.
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.
INT priority bits 2:0. These bits indicate the source for a pending
interrupt at interrupt priority levels 1, 2, and 3 (see
INT status
0
0
1
0
0
0
0
logic 0 or cleared = default condition
logic 0 or cleared = default condition
logic 0 or cleared = default condition
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 (normal default condition)
Dual UART with 32-byte FIFOs and IrDA encoder/decoder
1
1
1
0
0
0
0
1
0
0
1
0
0
0
0
0
0
0
0
0
0
Table 14 “Interrupt source”
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
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
SC68C652B
Table
14).
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