ADE7569 datasheet(84/136 Pages) AD

84 / 136 page

ADE7566/ADE7569

Preliminary Technical Data

Rev. PrA | Page 84 of 136

INTERRUPT VECTORS

When an interrupt occurs, the program counter is pushed onto

the stack, and the corresponding interrupt vector address is loaded

into the program counter. When the interrupt service routine is

complete, the program counter is popped off the stack by a RETI

instruction. This allows program execution to resume from where

it was interrupted. The interrupt vector addresses are shown in

Table 70.

Table 70. Interrupt Vector Addresses

Source

Vector Address

IE0

0x0003

TF0

0x000B

IE1

0x0013

TF1

0x001B

RI + TI

0x0023

TF2 + EXF2

0x002B

ITEMP (Temperature ADC)

0x0033

ISPI/I2CI

0x003B

IPSM (Power Supply)

0x0043

IADE (Energy Measurement DSP)

0x004B

IRTC (RTC Interval Timer)

0x0053

WDT (Watchdog Timer)

0x005B

INTERRUPT LATENCY

The 8051 architecture requires that at least one instruction

execute between interrupts. To ensure this, the 8051 MCU

core hardware prevents the program counter from jumping to

an ISR immediately after completing a RETI instruction or an

access of the IP and IE registers.

The shortest interrupt latency is 3.25 instruction cycles, 800 ns

with a clock of 4.096 MHz. The longest interrupt latency for a

high priority interrupt results when a pending interrupt is

generated during a low priority interrupt RETI, followed by a

multiply instruction. This results in a maximum interrupt

latency of 16.25 instruction cycles, 4 μs with a clock of 4.096 MHz.

CONTEXT SAVING

When the 8052 vectors to an interrupt, only the program counter

is saved on the stack. Therefore, the interrupt service routine

must be written to ensure that registers used in the main

program are restored to their pre-interrupt state. Common

registers that can be modified in the ISR are the accumulator

that are used as scratchpads in the ISR should also be restored

before exiting the interrupt. The following example 8051 code

shows how to restore some commonly used registers:

GeneralISR:

; save the current Accumulator value

PUSH

ACC

; save the current status and register

bank selection

PUSH

PSW

; service interrupt

…

; restore the status and register bank

selection

POP

PSW

; restore the accumulator

POP

ACC

RETI

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