AD7643BSTZ datasheet(23/29 Pages) AD

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AD7643

Rev. 0 | Page 22 of 28

16-Bit and 8-Bit Interface (Master or Slave)

In the 16-bit (MODE[1:0] = 1) and 8-bit (MODE[1:0] = 2)

interfaces, the A0/A1 pins allow a glueless interface to a 16- or

8-bit bus, as shown in Figure 35. By connecting A0/A1 to an

address line(s), the data can be read in two words for a 16-bit

interface, or three bytes for an 8-bit interface. This interface can

be used in both master and slave parallel reading modes. Refer

to Table 7 for the full details of the interface.

CS, RD

D[17:2]

HI-Z

HIGH

WORD

LOW

WORD

HI-Z

t12

t13

HIGH

BYTE

MID

BYTE

LOW

BYTE

D[17:10]

t12

HI-Z

t12

Figure 35. 8-Bit and 16-Bit Parallel Interface

SERIAL INTERFACE

The AD7643 is configured to use the serial interface when

MODE[1:0] = 3. The AD7643 outputs 18 bits of data, MSB first,

on the SDOUT pin. This data is synchronized with the 18 clock

pulses provided on the SCLK pin. The output data is valid on

both the rising and falling edge of the data clock.

MASTER SERIAL INTERFACE

Internal Clock

The AD7643 is configured to generate and provide the serial

data clock SCLK when the EXT/INT pin is held low. The

AD7643 also generates a SYNC signal to indicate to the host

when the serial data is valid. The serial clock SCLK and the

SYNC signal can be inverted. Depending on the read during

convert input, RDC/SDIN, the data can be read after each

conversion or during the following conversion. Figure 36 and

Figure 37 show detailed timing diagrams of these two modes.

Usually, because the AD7643 is used with a fast throughput, the

master read during conversion mode is the most recommended

serial mode. In this mode, the serial clock and data toggle at

appropriate instants, minimizing potential feedthrough between

digital activity and critical conversion decisions. In this mode,

the SCLK period changes because the LSBs require more time

to settle and the SCLK is derived from the SAR conversion cycle.

In read after conversion mode, it should be noted that unlike

other modes, the BUSY signal returns low after the 18 data bits

are pulsed out and not at the end of the conversion phase,

resulting in a longer BUSY width. As a result, the maximum

throughput cannot be achieved in this mode.

In addition, in read after convert mode, the SCLK frequency

can be slowed down to accommodate different hosts using the

DIVSCLK[1:0] inputs. Refer to Table 4 for the SCLK timing

details when using these inputs.

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