Datasheet

ADE7116/ADE7156/ADE7166/ADE7169/ADE7566/ADE7569
Rev. B | Page 97 of 152
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 an RETI instruction. This allows program execution to resume
from where it was interrupted. The interrupt vector addresses
are shown in Table 84.
Table 84. Interrupt Vector Addresses
Source Vector Address
IE0 0x0003
TF0 0x000B
IE1 0x0013
TF1 0x001B
RI + TI 0x0023
TF2 + EXF2 0x002B
ITEMP (Temperature ADC)
1
0x0033
ISPI/I2CI 0x003B
IPSM (Power Supply) 0x0043
IADE (Energy Measurement DSP) 0x004B
IRTC (RTC Interval Timer) 0x0053
WDT (Watchdog Timer) 0x005B
1
This feature is not available in the ADE7116.
INTERRUPT LATENCY
The 8052 architecture requires that at least one instruction
execute between interrupts. To ensure this, the 8052 MCU
core hardware prevents the program counter from jumping to
an ISR immediately after completing an RETI instruction or an
access of the IP and IE SFRs.
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
SFRs that can be modified in the ISR are the accumulator
register and the PSW register. Any general-purpose registers
that are used as scratch pads in the ISR should also be restored
before exiting the interrupt. The following example 8052 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