AD7827

–10–

REV. 0

AD7827 SERIAL INTERFACE

In order to achieve a high throughput rate, the serial port of the

AD7827 has been optimized for high speed serial protocols.

Many high speed serial protocols use a continuous serial clock

to transfer data, e.g., the serial ports of many popular DSPs like

the TMS320C5x, ADSP-21xx and DSP560xx. The serial inter-

face of the AD7827 is optimized for communication with such

devices.

The serial interface of the AD7827 uses a three-wire interface to

communicate with a Master. The serial clock pin (SCLK) is a

logic input and determines the bit transfer rate. The Receive

Frame Synchronization pin (RFS) is a logic output and used to

synchronize the data with a continuous serial clock. The data

out onto this pin on the rising edge of the serial clock. The first

rising edge of the serial clock after the end of a conversion causes

leaves its high impedance state and the first MSB is shifted out

on the first SCLK rising edge after the end of conversion. The

remaining seven data bits are shifted out on subsequent SCLK

on the falling edge of the eighth SCLK after RFS goes low. The

RFS output goes high again on the rising edge of the ninth SCLK.

If the AD7827 does not receive a ninth SCLK, the RFS will be

reset logic high by the next falling edge of

CONVST.

DB7

DB6

DB5

DB4

DB3

DB2

DB1

DB0

RFS

SCLK

CONVST

1

2345

6

7

8

Figure 15. Serial Timing