Datasheet

Data Sheet ADE7854/ADE7858/ADE7868/ADE7878
Rev. G | Page 67 of 100
goes active low. The flag bits in the interrupt status register are set
irrespective of the state of the mask bits. To determine the source
of the interrupt, the MCU should perform a read of the corres-
ponding STATUSx register and identify which bit is set to 1. To
erase the flag in the status register, write back to the STATUSx
register with the flag set to 1. After an interrupt pin goes low, the
status register is read and the source of the interrupt is identified.
Then, the status register is written back without any change to
clear the status flag to 0. The
IRQx
pin remains low until the
status flag is cancelled.
By default, all interrupts are disabled. However, the RSTDONE
interrupt is an exception. This interrupt can never be masked
(disabled) and, therefore, Bit 15 (RSTDONE) in the MASK1
register does not have any functionality. The
IRQ1
pin always
goes low, and Bit 15 (RSTDONE) in the STATUS1 register is set
to 1 whenever a power-up or a hardware/software reset process
ends. To cancel the status flag, the STATUS1 register has to be
written with Bit 15 (RSTDONE) set to 1.
Certain interrupts are used in conjunction with other status
registers. The following bits in the MASK1 register work in
conjunction with the status bits in the PHNOLOAD register:
• Bit 0 (NLOAD)
• Bit1 (FNLOAD), available in the ADE7878 only
• Bit 2 (VAN LOA D)
The following bits in the MASK1 register work with the status bits
in the PHSTATUS register:
• Bit 16, (SAG)
• Bit 17 (OI)
• Bit 18 (OV)
The following bits in the MASK1 register work with the status bits
in the IPEAK and VPEAK registers, respectively:
• Bit 23 (PKI)
• Bit 24 (PKV)
The following bits in the MASK0 register work with the status bits
in the PHSIGN register:
• Bits[6:8] (REVAPx)
• Bits[10:12] (REVRPx), available in the ADE7858,
ADE7868, and ADE7878 only
• Bit 9, Bit 13, and Bit 18 (REVPSUMx)
When the STATUSx register is read and one of these bits is set
to 1, the status register associated with the bit is immediately
read to identify the phase that triggered the interrupt and only
at that time can the STATUSx register be written back with the bit
set to 1.
Using the Interrupts with an MCU
Figure 84 shows a timing diagram that illustrates a suggested
implementation of the ADE7854/ADE7858/ADE7868/ADE7878
interrupt management using an MCU. At Time t
1
, the
IRQx
pin
goes active low indicating that one or more interrupt events
have occurred in the ADE78xx, at which point the following
steps should be taken:
1. Tie the
IRQx
pin to a negative-edge-triggered external
interrupt on the MCU.
2. On detection of the negative edge, configure the MCU to
start executing its interrupt service routine (ISR).
3. On entering the ISR, disable all interrupts using the global
interrupt mask bit. At this point, the MCU external interrupt
flag can be cleared to capture interrupt events that occur
during the current ISR.
4. When the MCU interrupt flag is cleared, a read from
STATUSx, the interrupt status register, is carried out. The
interrupt status register content is used to determine the
source of the interrupt(s) and, hence, the appropriate
action to be taken.
5. The same STATUSx content is written back into the
ADE78xx to clear the status flag(s) and reset the
IRQx
line
to logic high (t
2
).
If a subsequent interrupt event occurs during the ISR (t
3
), that
event is recorded by the MCU external interrupt flag being set
again.
On returning from the ISR, the global interrupt mask bit is
cleared (same instruction cycle) and the external interrupt flag
uses the MCU to jump to its ISR once again. This ensures that
the MCU does not miss any external interrupts.
Figure 85 shows a recommended timing diagram when the
status bits in the STATUSx registers work in conjunction with
bits in other registers. When the
IRQx
pin goes active low, the
STATUSx register is read, and if one of these bits is 1, a second