ST52T400 datasheet(40/94 Pages) STMICROELECTRONICS

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4.5 Interrupt Priority

Seven priority levels are available: level 6 has the

lowest priority, level 0 has the highest priority.

Level 6 is associated to the Main Program, levels

5 to 1 are programmable by means of the priority

registers

called

REG_CONF17

and

REG_CONF18; whereas the higher level is

related to the External Interrupt (INT_EXT).

PWM/Timer, TRIAC/PWM and Analog Block are

identified by a three-bit Peripheral Code (see

Table 4.2); in order to set the

i-th priority level the

user must write the peripheral label

i in the related

INT

i priority level.

For instance:

LDRC 10,193

(loads the value 193=’11000001’

in the RAM Register 10)

LDRC 11,168

(loads the value 168=’10101000’

in the RAM Register 11)

LDCR 17,10

(REG_CONF17= ‘11000001’)

LDCR 18,11

(REG_CONF18= ‘10101000’)

thus defining the following priority levels:

Level 1: INT_PWM/TIMER (PWM/TIMER Code:

001)

Level 2: INT_ADC (ADC Code: 000)

Level 3: INT_TRIAC/PWM_R (TRIAC/PWM

Code: 011)

Level 4: INT_TRIAC/Ph (TRIAC/Ph Code: 100)

Level 5: INT_TRIAC/PWM_F (TRIAC/PWM_F

Code: 010)

REMARK:

The Interrupt priority must be set at the

beginning of the main program, because at the

RESET REG_CONF1=’00000000’, this condition

could

generate

wrong

operations.

Further,

changing the priority levels must be avoided in

interrupt service routines.

When a source provides an Interrupt request, and

the request processing is also enabled, the CU

changes the normal sequential flow of a program

by transferring program control to a selected ser-

vice routine.

When an interrupt occurs the CU executes a

JUMP instruction to the address loaded in the

related location of the Interrupt Vector and the

flags are saved.

When the execution returns to the original pro-

Figure 4.5 Interrupt Configuration Registers 17 and 18

INT 1

Not Used

INT 2

REG_CONF17

Interrupts Priority

D10

D11

D12

D13

D14

D15

REG_CONF18

INT 3

INT 5

INT 4

Table 4.3 Conf. Registers 17-18 Description

Bit

Name

Value

Level

0, 1, 2

INT1

Peripheral

High

3, 4, 5

INT2

Peripheral

MediumHigh

6, 7, 8

INT4

Peripheral

MediumLow

9, 10, 11

INT5

Peripheral

Low

12, 13,

INT6

Peripheral

Very Low

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