71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
When an interrupt occurs, the MPU will vector to the predetermined address as shown in Table 52. Once interrupt service has
begun, it can be interrupted only by a higher priority interrupt. The interrupt service is terminated by a return from instruction,
"RETI". When a RETI instruction is performed, the processor will return to the instruction that would have been next when the
interrupt occurred.
When the interrupt condition occurs, the processor will also indicate this by setting a flag bit. This bit is set regardless of
whether the interrupt is enabled or disabled. Each interrupt flag is sampled once per machine cycle, then samples are polled
by the hardware. If the sample indicates a pending interrupt when the interrupt is enabled, then the interrupt request flag is set.
On the next instruction cycle, the interrupt will be acknowledged by hardware forcing an LCALL to the appropriate vector
address, if the following conditions are met:
•
•
•
No interrupt of equal or higher priority is already in progress.
An instruction is currently being executed and is not completed.
The instruction in progress is not RETI or any write access to the registers IEN0, IEN1, IEN2, IP0 or IP1.
Special Function Registers for Interrupts:
Interrupt Enable 0 register (IE0)
MSB
LSB
EX0
EAL
WDT
ES0
ET1
EX1
ET0
Table 34: The IEN0 Register
Bit
Symbol Function
IEN0.7
IEN0.6
IEN0.5
IEN0.4
IEN0.3
IEN0.2
IEN0.1
IEN0.0
EAL
WDT
-
EAL=0 – disable all interrupts
Not used for interrupt control
ES0
ET1
EX1
ET0
EX0
ES0=0 – disable serial channel 0 interrupt
ET1=0 – disable timer 1 overflow interrupt
EX1=0 – disable external interrupt 1
ET0=0 – disable timer 0 overflow interrupt
EX0=0 – disable external interrupt 0
Table 35: The IEN0 Bit Functions
Interrupt Enable 1 Register (IEN1)
MSB
LSB
SWDT
EX6
EX5
EX4
EX3
EX2
Table 36: The IEN1 Register
Page: 30 of 97
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