ADE7759 Analog Devices, ADE7759 Datasheet - Page 27

• Manufacturer Part Number: ADE7759
• Description: Active Energy Metering IC with di/dt Sensor Interface
• Manufacturer: Analog Devices

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 ADE7759, 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 before it is transferred to
one of the ADE7759 on-chip registers. Although another byte
transfer to the serial port can start while the previous byte is
being transferred to an on-chip register, this second byte transfer
should not finish until at least 4 µs after the end of the previous
byte transfer. This functionality is expressed in the timing speci-
fication t
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 Register
Description section. 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 addressed 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
four LSBs of the first byte written to the ADE7759 would be the
four MSBs of the 12-bit word. Figure 45 illustrates this example.
Serial Read Operation
During a data read operation from the ADE7759, data is shifted
out at the DOUT logic output on the rising edge of SCLK. As
was the case with the data write operation, a data read must be
preceded with a write to the Communications register.
SCLK
DOUT
SCLK
DIN
DIN
CS
CS
6
—see Figure 44. If a write operation is aborted during
SCLK
DIN
t
t
1
1
1
0
X
0
0
t
2
X
0
0
t
3
COMMAND BYTE
COMMAND BYTE
MOST SIGNIFICANT BYTE
A4
X
A4
t
4
A3
A3
X
t
5
DB11
A2
A2
A1
DB10
A1
A0
A0
DB9
t
t
7
DB8
t
11
9
With the ADE7759 in communications mode (i.e., CS logic low),
an 8-bit write to the Communications register first takes place.
The MSB of this byte transfer is a 0, indicating that the next
data transfer operation is a read. The LSBs of this byte contain
the address of the register that is to be read. The ADE7759 starts
shifting out of the register data on the next rising edge of SCLK—
see Figure 46. At this point the DOUT logic output leaves its
high impedance state and starts driving the data bus. All remain-
ing bits of register data are shifted out on subsequent SCLK
rising edges. The serial interface also enters communications
mode again as soon as the read has been completed. At this
point the DOUT logic output enters a high impedance state on
the falling edge of the last SCLK pulse. The read operation may
be aborted by bringing the CS logic input high before the data
transfer is complete. The DOUT output enters a high imped-
ance state on the rising edge of CS.
When an ADE7759 register is addressed for a read operation,
the entire contents of that register are transferred to the serial
port. This allows the ADE7759 to modify its on-chip registers
without the risk of corrupting data during a multi byte transfer.
Note when a read operation follows a write operation, the read
command (i.e., write to Communications register) should not
happen for at least 4 µs after the end of the write operation. If the
read command is sent within 4 µs of the write operation, the last
byte of the write operation may be lost. This timing constraint is
given as timing specification t
DB7
DB7
DB7
MOST SIGNIFICANT BYTE
MOST SIGNIFICANT BYTE
DB6
DB5
LEAST SIGNIFICANT BYTE
DB4
t
11
DB0
DB0
DB3
t
t
7
10
9.
DB2
LEAST SIGNIFICANT BYTE
DB7
LEAST SIGNIFICANT BYTE
DB7
DB1
t
6
DB0
t
12
ADE7759
DB0
DB0
t
13
t
8