ADE7758 Analog Devices, ADE7758 Datasheet - Page 54

• Manufacturer Part Number: ADE7758
• Description: Poly Phase Multifunction Energy Metering IC with Per Phase Information
• Manufacturer: Analog Devices

ADE7758
Example—Calibration of RMS Offsets
For this example, I
V
With I
0x34266 in the AIRMS (0x0A) register and 0x10B0A3 in the
AVRMS (0x0D) register. At I
0x19F in AIRMS. At V
in the AVRMS register. These are the average value of 20
samples synchronous to the zero crossings of all three phases.
Using this data, −3d is written to AVRMSOS (0x33) and −1004d
is written to AIRMSOS (0x36) registers according to the
Equation 56 and Equation 57.
This example shows the calculations and measurements for
Phase A only. However, all three xIRMS and xVRMS registers
can be read simultaneously to compute the values for each
xIRMSOS and xVRMSOS register.
CHECKSUM REGISTER
The ADE7758 has a checksum register CHECKSUM[7:0]
(0x7E) to ensure the data bits received in the last serial read
operation are not corrupted. The 8-bit checksum register is
reset before the first bit (MSB of the register to be read) is put
on the DOUT pin. During a serial read operation, when each
data bit becomes available on the rising edge of SCLK, the bit is
added to the checksum register. In the end of the serial read
operation, the content of the checksum register is equal to the
sum of all the ones in the register previously read. Using the
checksum register, the user can determine if an error has
occurred during the last read operation. Note that a read to the
checksum register also generates a checksum of the checksum
register itself.
FULLSCALE
CONTENT OF REGISTERS
xIRMSOS
xVRMSOS
(
10
TEST
2
(N-BYTES)
Figure 85. Checksum Register for Serial Interface Read
= 500 V, Power Factor = 1, and Frequency = 50 Hz.
×
and V
415
2
=
(
0
=
) (
NOM
16
2 .
–
64
TEST
1
−
,
–
0
, the example ADE7758 meter shows
384
1
2 .
10
×
= 10 A, I
2
NOM/20
(
2
220
×
×
)
213
×
, the example meter shows 0xD65B
MAX/500
,
54875
606
MAX
(
2
11
)
, the example meter shows
= 100 A, V
) (
=
–
–
−
220
11
1103
CHECKSUM
REGISTER
×
)
, 1
.
093
88
NOM
=
,
795
DOUT
−
= 220 V,
1104
ADDR: 0x7E
)
=
−
. 3
047
Rev. A | Page 54 of 68
=
−
3
ADE7758 INTERRUPTS
The ADE7758 interrupts are managed through the interrupt
status register (STATUS[23:0], Address 0x19) and the interrupt
mask register (MASK[23:0], Address 0x18). When an interrupt
event occurs in the ADE7758, the corresponding flag in the
interrupt status register is set to a Logic 1 (see Table 20). If the
mask bit for this interrupt in the interrupt mask register is
Logic 1, then the IRQ logic output 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
system master (MCU) should perform a read from the reset
interrupt status register with reset. This is achieved by carrying
out a read from RSTATUS, Address 0x1A. The IRQ output goes
logic high on completion of the interrupt status register read
command (see the Interrupt Timing section). When carrying
out a read with reset, the ADE7758 is designed to ensure that no
interrupt events are missed. If an interrupt event occurs just as
the interrupt status register is being read, the event is not lost
and the IRQ logic output is guaranteed to go logic high for the
duration of the interrupt status register data transfer before
going logic low again to indicate the pending interrupt. Note
that the reset interrupt bit in the status register is high for only
one clock cycle; then it goes back to 0.
USING THE ADE7758 INTERRUPTS WITH AN MCU
Figure 87 shows a timing diagram that illustrates a suggested
implementation of ADE7758 interrupt management using an
MCU. At time t
one or more interrupt events have occurred in the ADE7758.
The IRQ logic output should be tied to a negative edge triggered
external interrupt on the MCU. On detection of the negative
edge, the MCU should be configured to start executing its
interrupt service routine (ISR). On entering the ISR, all
interrupts should be disabled using the global interrupt mask
bit. At this point, the MCU external interrupt flag can be
cleared in order to capture interrupt events that occur during
the current ISR. When the MCU interrupt flag is cleared, a read
from the reset interrupt status register with reset is carried out.
(This causes the IRQ line to be reset logic high (t
Interrupt Timing section.) The reset interrupt status register
contents are used to determine the source of the interrupt(s) and
hence the appropriate action to be taken. If a subsequent
interrupt event occurs during the ISR (t
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. The reset bit in the status
register is an exception to this, and is only high for one clock
cycle after a reset event.
1
, the IRQ line goes active low indicating that
3
) that event is recorded
2
)—see the