AD7654ASTZ datasheet(20/28 Pages) AD

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Data Sheet

AD7654

Rev. D | Page 19 of 27

t17

BUSY

DATA

BUS

t16

NEW A

OR B

PREVIOUS CHANNEL A

OR B

PREVIOUS CHANNEL B

OR NEW A

t10

CS = RD = 0

EOC

CNVST

Figure 25. Master Parallel Data Timing for Continuous Read

Slave Parallel Interface

In slave parallel reading mode, the data can be read either after

each conversion, which is during the next acquisition phase or

during the other channel’s conversion, or during the following

conversion, as shown in Figure 26 and Figure 27, respectively.

When the data is read during the conversion, however, it is

recommended that it is read only during the first half of the

conversion phase. This avoids any potential feedthrough between

voltage transients on the digital interface and the most critical

analog conversion circuitry.

DATA BUS

t18

t19

BUSY

CURRENT

CONVERSION

Figure 26. Slave Parallel Data Timing for a Read After Conversion

CONVERSION

t18

t19

BUSY

DATA BUS

t13

t11

t12

t10

CS =0

EOC

CNVST, RD

Figure 27. Slave Parallel Data Timing for a Read During Conversion

8-Bit Interface (Master or Slave)

The BYTESWAP pin allows a glueless interface to an 8-bit bus.

As shown in Figure 28, the LSB byte is output on D[7:0] and the

MSB is output on D[15:8] when BYTESWAP is low. When

BYTESWAP is high, the LSB and MSB bytes are swapped, the

LSB is output on D[15:8], and the MSB is output on D[7:0]. By

connecting BYTESWAP to an address line, the 16-bit data can

be read in two bytes on either D[15:8] or D[7:0].

BYTESWAP

PINS D[15:8]

PINS D[7:0]

HI-Z

HIGH BYTE

LOW BYTE

HIGH BYTE

HI-Z

t18

t19

Figure 28. 8-Bit Parallel Interface

Channel A/B Output

The A/B input controls which channel’s conversion results

(INAx or INBx) are output on the data bus. The functionality of

A/B is detailed in Figure 29. When high, the data from Channel A

is available on the data bus. When low, the data from Channel B

is available on the bus. Note that Channel A can be read

immediately after conversion is done (EOC), while Channel B is

still in its converting phase. However, in any of the serial reading

modes, Channel A data is updated only after Channel B is

converted.

t18

t20

DATA BUS

HI-Z

A/B

HI-Z

CHANNEL A

CHANNEL B

Figure 29. A/B Channel Reading

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