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C167CS

Derivatives

Interrupt and Trap Functions

User’s Manual

5-6

V2.0, 2000-07

Normal Interrupt Processing and PEC Service

During each instruction cycle one out of all sources which require PEC or interrupt

processing is selected according to its interrupt priority. This priority of interrupts and

PEC requests is programmable in two levels. Each requesting source can be assigned

to a specific priority. A second level (called “group priority”) allows to specify an internal

order for simultaneous requests from a group of different sources on the same priority

level. At the end of each instruction cycle the one source request with the highest current

priority will be determined by the interrupt system. This request will then be serviced, if

its priority is higher than the current CPU priority in register PSW.

Interrupt System Register Description

Interrupt processing is controlled globally by register PSW through a general interrupt

enable bit (IEN) and the CPU priority field (ILVL). Additionally the different interrupt

sources are controlled individually by their specific interrupt control registers (… IC).

Thus, the acceptance of requests by the CPU is determined by both the individual

interrupt control registers and the PSW. PEC services are controlled by the respective

PECCx register and the source and destination pointers, which specify the task of the

respective PEC service channel.

5.1.1

Interrupt Control Registers

All interrupt control registers are organized identically. The lower 8 bits of an interrupt

control register contain the complete interrupt status information of the associated

source, which is required during one round of prioritization, the upper 8 bits of the

respective register are reserved. All interrupt control registers are bit-addressable and all

bits can be read or written via software. This allows each interrupt source to be

programmed or modified with just one instruction. When accessing interrupt control

registers through instructions which operate on word data types, their upper 8 bits

(15 … 8) will return zeros, when read, and will discard written data.

The layout of the Interrupt Control registers shown below applies to each xxIC register,

where xx stands for the mnemonic for the respective source.

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