SC28L201 datasheet(69/110 Pages) NXP

69 / 110 page

9397 750 13138

Product data sheet

Rev. 01 — 31 October 2005

69 of 110

Philips Semiconductors

SC28L201

3.3 V, 5 V UART, 3.125 Mbit/s, with 256-byte FIFO

8.5 Registers of the Arbitrating Interrupt system and bidding control

8.5.1 Interrupt Control Register (ICR)

This register provides a single 8-bit ﬁeld called the interrupt threshold for use by the

interrupt arbiter. The ﬁeld is interpreted as a single unsigned integer. The interrupt arbiter

will not generate an external interrupt request, by asserting IRQN, unless the value of the

highest priority interrupt exceeds the value of the interrupt threshold. If the highest bidder

in the interrupt arbitration is lower than the threshold level set by the ICR, the Current

Interrupt Register, CIR, will contain 0x00.

Remark: While a Watchdog Timer interrupt is pending, the ICR is not used and only

receiver codes are presented for interrupt arbitration. This allows receivers with very low

count values (perhaps below the threshold value) to win interrupt arbitration without

requiring the user to explicitly lower the threshold level in the ICR.

8.5.2 Update CIR (UCIR): the most important command for polled or interrupt

service

A write to address 0x61 data is not important. A command based upon a decode of a

write to address 0x61 (UCIR is not a register). A write (the write data is not important; a

‘Don’t care’) to this ‘register’ causes the Current Interrupt Register to be updated with the

value that is winning interrupt arbitration. The register would be used in systems that poll

the interrupt status registers rather than wait for interrupts. Alternatively, the CIR is

normally updated during an Interrupt Acknowledge Bus (IACKN) cycle in interrupt-driven

systems.

Table 46:

ICR - Interrupt Control Register (address 0x60) bit description

Bit

Symbol

Description

7:0

Upper 8 bits of the Arbitration Threshold

Table 47:

UCIR - Update CIR (address 0x61) bit description

Bit

Symbol

Description

7:0

data not important

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