ADE7754 Analog Devices, ADE7754 Datasheet - Page 31

• Manufacturer Part Number: ADE7754
• Description: Poly-phase Multi-Function Energy Metering IC with Serial Port
• Manufacturer: Analog Devices

ADE7754 SERIAL INTERFACE
ADE7754 has a built-in SPI interface. The Serial Interface
of the ADE7754 is made of four signals SCLK, DIN,
DOUT and CS. The serial clock for a data transfer is applied
at the SCLK logic input. This logic input has a Schmidt-
trigger input structure, which allows slow rising (and falling)
clock edges to be used. All data transfer operations are
synchronized to the serial clock. Data is shifted into the
ADE7754 at the DIN logic input on the falling edge of
SCLK. Data is shifted out of the ADE7754 at the DOUT
logic output on a rising edge of SCLK. The CS logic input
is the chip select input. This input is used when multiple
devices share the serial bus. A falling edge on CS also resets
the serial interface and places the ADE7754 in communica-
tions mode. The CS input should be driven low for the entire
data transfer operation. Bringing CS high during a data
transfer operation will abort the transfer and place the serial
bus in a high impedance state. The CS logic input may be tied
low if the ADE7754 is the only device on the serial bus.
However with CS tied low, all initiated data transfer opera-
tions must be fully completed, i.e., the LSB of each register
must be transferred as there is no other way of bringing the
ADE7754 back into communications mode without resetting
the entire device, i.e., setting the RESET pin logic low.
All the ADE7754 functionality is accessible via several on-
chip registers – see Figure 39. The contents of these registers
can be updated or read using the on-chip serial interface.
After power-on or toggling the RESET pin low or a falling
edge on CS, the ADE7754 is placed in communications
mode. In communications mode the ADE7754 expects the
first communication to be a write to the internal Communi-
cations register. The data written to the Communications
register contains the address and specifies the next data
transfer to be a read or a write command. Therefore all data
transfer operations with the ADE7754, whether a read or a
write, must begin with a write to the Communications
register.
The Communications register is an eight bit write only
register. The MSB determines whether the next data transfer
operation is a read or a write. The 6 LSBs contain the address
of the register to be accessed. See ADE7754 Communications
Register for a more detailed description.
Figure 40 and Figure 41 show the data transfer sequences for
a read and write operation respectively.
On completion of a data transfer (read or write) the ADE7754
once again enters communications mode, i.e. the next in-
REV. PrG 01/03
Figure 39– Addressing ADE7754 Registers via the
DOUT
DIN
Communications Register
COMMUNICATIONS REGISTER
REGISTER # n-1
PRELIMINARY TECHNICAL DATA
REGISTER # n
REGISTER # 1
REGISTER # 2
REGISTER # 3
OUT
OUT
OUT
OUT
OUT
IN
IN
IN
IN
IN
–31–
struction followed must be a write to the Communications
register.
A data transfer is completed when the LSB of the ADE7754
register being addressed (for a write or a read) is transferred
to or from the ADE7754.
ADE7754 Serial Write Operation
The serial write sequence takes place as follows: with the
ADE7754 in communications mode and the CS input logic
low, a write to the communications register first takes place.
The MSB of this byte transfer must be set to 1, indicating that
the next data transfer operation is a write to the register. The
six LSBs of this byte contain the address of the register to be
written to. The ADE7754 starts shifting in the register data
on the next falling edge of SCLK. All remaining bits of
register data are shifted in on the falling edge of subsequent
SCLK pulses – see Figure 42.
As explained earlier the data write is initiated by a write to the
Communications register followed by the data. During a data
write operation to the ADE7754, data is transferred to all on-
chip registers one byte at a time. After a byte is transferred
into the serial port, there is a finite time duration before the
content in the serial port buffer is transferred to one of the
ADE7754 on-chip registers. Although another byte transfer
to the serial port can start while the previous byte is being
transferred to the destination register, this second byte
transfer should not finish until at least TBD after the end of
the previous byte transfer. This functionality is expressed in
the timing specification t
is aborted during a byte transfer (CS brought high), then that
byte will not be written to the destination register.
Destination registers may be up to 3 bytes wide – see
ADE7754 Register Descriptions. Hence the first byte shifted
into the serial port at DIN is transferred to the MSB (Most
significant Byte) of the destination register. If the destination
register is 12 bits wide, for example, a two-byte data transfer
must take place. The data is always assumed to be right
justified, therefore in this case, the four MSBs of the first byte
would be ignored and the 4 LSBs of the first byte written to
the ADE7754 would be the 4MSBs of the 12-bit word.
Figure 43 illustrates this example.
SCLK
DOUT
SCLK
DIN
DIN
CS
CS
Figure 40 – Reading data from the ADE7754 via the
COMMUNICATIONS REGISTER WRITE
COMMUNICATIONS REGISTER WRITE
Figure 41 – Writing data to the ADE7754 via the
1 0
0 0
ADDRESS
ADDRESS
serial interface
serial interface
6
- see Figure 42. If a write operation
MULTIBYTE WRITE DATA
MULTIBYTE READ DATA
ADE7754