ADE7754_15 datasheet(29/44 Pages) AD

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REV. 0

ADE7754

–29–

SCLK

DIN

DB7

MOST SIGNIFICANT BYTE

t2 t3

DB0

DB7

DB0

LEAST SIGNIFICANT BYTE

COMMAND BYTE

Figure 44. Serial Interface Write Timing Diagram

SCLK

DB11 DB10

DB9

DB8

DIN

MOST SIGNIFICANT BYTE

DB3

DB2

DB1

DB0

DB7

DB6

DB5

DB4

LEAST SIGNIFICANT BYTE

Figure 45. 12-Bit Serial Write Operation

Serial Read Operation

During a data read operation from the ADE7754, 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 by a write to the communications register.

With the ADE7754 in communications mode and

CS logic low,

an 8-bit write to the communications register first takes place.

The MSB of this byte transfer must be a 0, indicating that the

next data transfer operation is a read. The six LSBs of this byte

contain the address of the register to be read. The ADE7754

starts shifting out of the register data on the next rising edge of

SCLK. See Figure 46. At this point, the DOUT logic output

switches from high impedance state and starts driving the data

bus. All remaining bits of register data are shifted out on subsequent

SCLK rising edges. The serial interface enters communications

mode again as soon as the read has been completed. 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 com-

pleted. The DOUT output enters a high impedance state on the

rising edge of

CS.

When an ADE7754 register is addressed for a read operation,

the entire contents of that register are transferred to the serial

port. This allows the ADE7754 to modify its on-chip registers

without the risk of corrupting data during a multibyte transfer.

Note that when a read operation follows a write operation, the

read command (i.e., write to communications register) should

not happen for at least 1

µs after the end of the write operation.

If the read command is sent within 1

µs of the write operation,

the last byte of the write operation may be lost.

SCLK

DIN

t11

t12

DB7

DOUT

t13

DB0

DB7

t10

MOST SIGNIFICANT BYTE

LEAST SIGNIFICANT BYTE

COMMAND BYTE

Figure 46. Serial Interface Read Timing Diagram

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