EVAL-ADE7880EBZ datasheet(38/104 Pages) AD

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ADE7880

Data Sheet

Rev. A | Page 38 of 104

REFERENCE CIRCUIT

The nominal reference voltage at the REFIN/OUT pin is 1.2 ±

0.075% V. This is the reference voltage used for the ADCs in

the ADE7880. The REFIN/OUT pin can be overdriven by an

external source, for example, an external 1.2 V reference.

The voltage of the ADE7880 reference drifts slightly with

temperature; see the Specifications section for the temperature

coefficient specification (in ppm/°C). The value of the temperature

drift varies from part to part. Because the reference is used for

all ADCs, any x percentage drift in the reference results in a 2×

percentage deviation of the meter accuracy. The reference drift

resulting from temperature changes is usually very small and

typically much smaller than the drift of other components on a

meter. Alternatively, the meter can be calibrated at multiple

temperatures.

If Bit 0 (EXTREFEN) in the CONFIG2 register is cleared to 0 (the

default value), the ADE7880 uses the internal voltage reference.

If the bit is set to 1, the external voltage reference is used. Set the

CONFIG2 register during the PSM0 mode. Its value is maintained

during the PSM1, PSM2, and PSM3 power modes.

DIGITAL SIGNAL PROCESSOR

The ADE7880 contains a fixed function digital signal processor

(DSP) that computes all powers and rms values. It contains

program memory ROM and data memory RAM.

The program used for the power and rms computations is

stored in the program memory ROM and the processor executes

it every 8 kHz. The end of the computations is signaled by

setting Bit 17 (DREADY) to 1 in the STATUS0 register. An

interrupt attached to this flag can be enabled by setting Bit 17

(DREADY) in the MASK0 register. If enabled, the IRQ0 pin is

set low and Status Bit DREADY is set to 1 at the end of the

computations. The status bit is cleared and the IRQ0 pin is set

to high by writing to the STATUS0 register with Bit 17 (DREADY)

set to 1.

The registers used by the DSP are located in the data memory

RAM, at addresses between 0x4380 and 0x43BE. The width of

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

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 (between Address 0x4380 and Address

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

three times 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.

•

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.

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:

EVAL-ADE7880EBZ 数据表(PDF) 38 Page - Analog Devices

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