ADS1294 datasheet(43/88 Pages) TI

43 / 88 page

Hi-Z

START

DRDY

SCLK

DIN

DOUT

RDATAOpcode

Status Register+8-ChannelData(216Bits)

RDATAOpcode

ADS1294, ADS1294R

ADS1296, ADS1296R

ADS1298, ADS1298R

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SBAS459H

– JANUARY 2010 – REVISED OCTOBER 2011

RDATA: Read Data

Issue this command after DRDY goes low to read the conversion result (in Stop Read Data Continuous mode).

There is no restriction on the SCLK rate for this command, and there is no wait time needed for the subsequent

commands or data retrieval SCLKs. To retrieve data from the device after RDATA command is issued, make

sure either the START pin is high or the START command is issued. When reading data with the RDATA

command, the read operation can overlap the occurrence of the next DRDY without data corruption. Figure 48

shows the recommended way to use the RDATA command. RDATA is best suited for ECG- and EEG-type

systems where register settings must be read or changed often between conversion cycles.

Figure 48. RDATA Usage

Sending Multi-Byte Commands

The ADS129x serial interface decodes commands in bytes and requires 4 tCLK cycles to decode and execute.

Therefore, when sending multi-byte commands, a 4 tCLK period must separate the end of one byte (or opcode)

and the next.

Assume CLK is 2.048MHz, then tSDECODE (4 tCLK) is 1.96µs. When SCLK is 16MHz, one byte can be transferred

in 500ns. This byte transfer time does not meet the tSDECODE specification; therefore, a delay must be inserted so

the end of the second byte arrives 1.46

µs later. If SCLK is 4MHz, one byte is transferred in 2µs. Because this

transfer time exceeds the tSDECODE specification, the processor can send subsequent bytes without delay. In this

later scenario, the serial port can be programmed to cease single-byte transfer per cycle to multiple bytes.

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ADS1294 Datasheet(PDF) 43 Page - Texas Instruments