AD7655AST datasheet(19/28 Pages) AD

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AD7655

Rev. B | Page 19 of 28

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 24 and Figure 25, 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 24. Slave Parallel Data Timing for Reading (Read after Convert)

CONVERSION

t18

t19

BUSY

DATA BUS

t13

t11

t12

t10

CS = 0

EOC

CNVST, RD

Figure 25. Slave Parallel Data Timing for Reading (Read During Convert)

8-Bit Interface (Master or Slave)

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

As shown in Figure 26, 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 2 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 26. 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 function-ality

of A/B is detailed in Figure 27. 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 in parallel reading

mode, Channel A can be read immediately after the end of

conversion (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 conversion.

t18

t20

DATA BUS

HI-Z

A/B

HI-Z

CHANNEL A

CHANNEL B

Figure 27. A/B Channel Reading

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