ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 36

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

ADE7880
this memory is 28 bits. A two-stage pipeline is used when write
operations to the data memory RAM are executed. This means
two things: when only one register needs to be initialized, write
it two more times to ensure the value has been written into
RAM. When two or more registers need to be initialized, write
the last register in the queue two more times to ensure the value
has been written into RAM.
As explained in the Power-Up Procedure section, at power-up
or after a hardware or software reset, the DSP is in idle mode.
No instruction is executed. All the registers located in the data
memory RAM are initialized at 0, their default values and they
can be read/written without any restriction. The RUN register,
used to start and stop the DSP, is cleared to 0x0000. The RUN
register needs to be written with 0x0001 for the DSP to start
code execution. It is recommended to first initialize all ADE7880
registers located in the data memory RAM with their desired
values. Next, write the last register in the queue two additional
times to flush the pipeline and then write the RUN register with
0x0001. In this way, the DSP starts the computations from a
desired configuration.
To protect the integrity of the data stored in the data memory
RAM of the DSP (addresses between 0x4380 and 0x43BE), a
write protection mechanism is available. By default, the
protection is disabled and registers placed between 0x4380 and
0x43BE can be written without restriction. When the protection
is enabled, no writes to these registers is allowed. Registers can
be always read, without restriction, independent of the write
protection state. To enable the protection, write 0xAD to an
internal 8-bit register located at address 0xE7FE, followed by a
write of 0x80 to an internal 8-bit register located at address
0xE7E3. To disable the protection, write 0xAD to an internal 8-
bit register located at address 0xE7FE, followed by a write of
0x00 to an internal 8-bit register located at address 0xE7E3. It is
recommended to enable the write protection before starting the
DSP. If any data memory RAM based register needs to be
changed, simply disable the protection, change the value and
then enable back the protection. There is no need to stop the
DSP in order to change these registers.
The recommended procedure to initialize the registers located
in the data memory RAM is:
•
•
•
Initialize all registers. Write the last register in the queue 3
times in order to ensure its value was written into the
RAM. All the other registers of the ADE7880 should also
be initialized here.
Enable the write protection by writing 0xAD to an internal
8-bit register located at address 0xE7FE, followed by a
write of 0x80 to an internal 8-bit register located at address
0xE7E3.
Read back all data memory RAM registers to ensure they
were initialized with the desired values.
Rev. PrE | Page 36 of 103
•
•
There is no obvious reason to stop the DSP if the ADE7880 is
maintained in PSM0 normal mode. All ADE7880 registers,
including ones located in the data memory RAM, can be
modified without stopping the DSP. However, to stop the DSP,
0x0000 has to be written into RUN register. To restart the DSP,
one of the following procedures must be followed:
•
•
As mentioned in the Power Management section, when the
ADE7880 switch out of PSM0 power mode, it is recommended to
stop the DSP by writing 0x0000 into the run register (see Table
10 and Table 11 for the recommended actions when changing
power modes).
ROOT MEAN SQUARE MEASUREMENT
Root mean square (rms) is a measurement of the magnitude of
an ac signal. Its definition can be both practical and mathematical.
Defined practically, the rms value assigned to an ac signal is the
amount of dc required to produce an equivalent amount of
power in the load. Mathematically, the rms value of a conti-
nuous signal f(t) is defined as
For time sampling signals, rms calculation involves squaring the
signal, taking the average, and obtaining the square root.
Equation 10 implies that for signals containing harmonics, the
rms calculation contains the contribution of all harmonics, not
only the fundamental. The ADE7880 uses two different methods
to calculate rms values. The first one is very accurate and is active
only in PSM0 mode. The second one is less accurate, uses the
In the remote case one or more registers are not initialized
correctly, disable the protection by writing 0xAD to an
internal 8-bit register located at address 0xE7FE, followed
by a write of 0x00 to an internal 8-bit register located at
address 0xE7E3. Initialize again the registers. Write the last
register in the queue three times. Enable the write
protection by writing 0xAD to an internal 8-bit register
located at address 0xE7FE, followed by a write of 0x80 to
an internal 8-bit register located at address 0xE7E3..
Start the DSP by setting RUN=1.
If the ADE7880 registers located in the data memory RAM
have not been modified, write 0x0001 into the run register to
start the DSP.
If the ADE7880 registers located in the data memory RAM
have to be modified, first execute a software or a hardware
reset, initialize all ADE7880 registers at desired values,
enable the write protection and then write 0x0001 into the
RUN register to start the DSP.
F
F
rms
rms
=
=
1
t
N
1
∫
0
t
N
∑
N
f
=
Preliminary Technical Data
2
1
f
( )
t
2
[ ]
dt
n
(10)
(9)