ST20-GP1 datasheet(31/116 Pages) STMICROELECTRONICS

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ST20-GP1

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5.6

Interrupt conﬁguration registers

The interrupt controller is allocated a 4k block of memory in the internal peripheral address space.

Information on interrupts is stored in registers as detailed in the following section. The registers can

be examined and set by the

devlw (device load word) and devsw (device store word) instructions.

Note, they can not be accessed using memory instructions.

HandlerWptr register

The HandlerWptr registers (1 per interrupt) contain a pointer to the workspace of the interrupt

handler.

Note, before the interrupt is enabled, by writing a 1 in the Mask register, the user (or toolset) must

ensure that there is a valid Wptr in the register.

TriggerMode register

Each interrupt channel can be programmed to trigger on rising/falling edges or high/low levels on

the external Interrupt.

Note, level triggering is different to edge triggering in that if the input is held at the triggering level, a

continuous stream of interrupts is generated.

Mask register

An interrupt mask register is provided in the interrupt controller to selectively enable or disable

external interrupts. This mask register also includes a global interrupt disable bit to disable all

external interrupts whatever the state of the individual interrupt mask bits.

To complement this the interrupt controller also includes an interrupt pending register which

contains a pending ﬂag for each interrupt channel. The Mask register performs a masking function

on the Pending register to give control over what is allowed to interrupt the CPU while retaining the

ability to continually monitor external interrupts.

HandlerWptr0-4

Interrupt controller base address + #00 to #10

Read/Write

Bit

Bit field

Function

31:2

HandlerWptr

Pointer to the workspace of the interrupt handler.

1:0

RESERVED. Write 0.

Table 5.1 HandlerWptr register format — one register per interrupt

TriggerMode0-4

Interrupt controller base address + #40 to #50

Read/Write

Bit

Bit field

Function

2:0

Trigger

Control the triggering condition of the Interrupt, as follows:

Trigger2:0

Interrupt triggers on

000

No trigger mode

001

High level - triggered while input high

010

Low level - triggered while input low

011

Rising edge - low to high transition

100

Falling edge - high to low transition

101

Any edge - triggered on rising and falling edges

110

No trigger mode

111

No trigger mode

Table 5.2 TriggerMode register format — one register per interrupt

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