P90CE201 데이터 시트보기 (PDF) - Philips Electronics

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P90CE201

16-bit microcontroller

Philips Electronics 

Philips Semiconductors

16-bit microcontroller

Product specification

P90CE201

bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

FORMAT CODE 0 0

VECTOR NUMBER

00

FORMAT CODE

either 0000

or 1111

INFORMATION STACKED

Short Format (4 words)

68070 Format (17 words)

MCD514

Fig.9 Vector number and format code.

5.6 CPU interrupt processing

An Interrupt Controller handles all interrupts, solves any

priority problems and passes the highest level interrupt to

the CPU. The general interrupt handling mechanism and

the Interrupt Controller are described in section 6.2.

The CPU interrupt handling follows the same basic rules

as in the 68000. However, the following changes have

been made to simplify system development:

• Interrupts with a priority level equal to or less than the

priority level actually running will not be accepted.

• During the acknowledge cycle of an interrupt, the IPL

bits of the Status Register are set to the priority level of

the acknowledged interrupt. An exception to this is when

the IM bit in SYSCON2 is a logic 0. In this case level 7

is loaded into the Status Register. See section 6.1.2.

If the priority of the interrupt pending is greater than the

current processor priority then:

• The exception processing sequence is started.

• A copy of the Status Register is saved.

• The privilege level is set to supervisor state.

• Tracing is suppressed.

• The priority level of the processor is set to that of the

interrupt being acknowledged.

The processor then gets the vector number from the

interrupting device, classifies it as an interrupt

acknowledge, and displays the interrupt level number

being acknowledged on the address bus.

If autovectoring is requested by the interrupting device, the

processor internally generates a vector number that

corresponds to the interrupt level number.

The processor then starts normal exception processing by

saving the format word, Program Counter, and Status

Register in the supervisor stack. The value of the vector in

the format word is either supplied externally by the

requesting device or is an internally generated vector

number multiplied by four (format is all zeros). The

Program Counter value is the address of the instruction

that would have been executed if the interrupt had not

been present. Then the interrupt vector contents are

fetched and loaded into the Program Counter. The

interrupt handling routine starts with normal instruction

execution.

Priority level 7 is a special case; it can only be detected if

the priority level was set to a lower value in between.

August 1993

16

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