ST52F510 datasheet(40/106 Pages) STMICROELECTRONICS

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5 INTERRUPTS

The Control Unit (CU) responds to peripheral

events and external events through its interrupt

channels.

When such events occur, if the related interrupt is

not masked and doesn’t have a priority order, the

current program execution can be suspended to

allow the CU to execute a specific response

routine.

Each interrupt is associated with an interrupt

vector that contains the memory address of the

related interrupt service routine. Each vector is

located in the Program/Data Memory space at a

fixed address (see Figure 3.2 Program/Data

Memory Organization).

5.1 Interrupt Processing

If interrupts are pending at the end of an arithmetic

or logic instruction, the interrupt with the highest

priority is acknowledged. When the interrupt is

acknowledged the flags and the current PC are

saved in the stacks and the associated Interrupt

routine is executed. The start address of this

routine (Interrupt Vector) is located in three bytes

of the Program/Data Memory between address 3

and 32 (03h-020h). See Table 5.1 for the list of the

Interrupt Vector addresses.

The Interrupt routine is performed as a normal

code. At the end of each instruction, the CU checks

if a higher priority interrupt has sent an interrupt

request. An Interrupt request with a higher priority

stops lower priority Interrupts. The Program

Counter and the flags are stored in their own

stacks.

With the instruction RETI (Return from Interrupt)

the flags and the Program Counter (PC) are

restored from the top of the stacks. These stacks

have already been described in Paragraph 3.4.

An Interrupt request cannot stop fuzzy rule

processing, but only after the end of a fuzzy rule or

at the end of a logic or arithmetic instruction,

unless a Global Interrupt Disable instruction has

been executed before (see below).

Remark: A fuzzy routine can be interrupted only in

the Main program. When a Fuzzy function is

running inside another interrupt routine an interrupt

request can cause side effects in the Control Unit.

For this reason, in order to use a Fuzzy function

inside an interrupt routine, the user MUST include

the Fuzzy function between an UDGI (MDGI)

instruction and an UEGI (MEGI) instruction (see

the following paragraphs), in order to disable the

interrupt request during the execution of the fuzzy

function.

Figure 5.1 Interrupt Flow

5.2 Global Interrupt Request Enabling

When an Interrupt occurs, it generates a Global

Interrupt Pending (GIP). After a GIP a Global

Interrupt Request (GIR) will be generated and

Interrupt Service Routine associated with the

interrupt with higher priority will start.

In order to avoid possible conflicts between the

interrupt masking set in the main program, or

inside high level language compiler macros, the

GIP is put in AND through the User Global Interrupt

Mask or the Macro Global Interrupt Mask (see

Figure 5.2).

The UEGI/UDGI instruction switches the User

Global Interrupt Mask enabling/disabling the GIR

for the main program.

MEGI/MDGI instructions switch the Macro Global

Interrupt Mask on/off in order to ensure that the

macro will not be interrupted.

Figure 5.2 Global Interrupt Request

NORMAL

PROGRAM

FLOW

INTERRUPT

SERVICE

ROUTINE

RETI

INSTRUCTION

INTERRUPT

Global Interrupt

Pending

User Global

Interrupt Mask

Macro Global

Global Interrupt

Request

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