AFE5804 datasheet(29/60 Pages) TI

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SERIAL INTERFACE

Serial Port Interface (SPI) Information

(connectexternally)

VCA_CS

RST

[H4]

[H9]

VCA_SCLK

VCA_SDATA

ADS_CS

ADS_SCLK

ADS_SDATA

ADS_RESET

[H8]

SDATA

[H76]

[H6]

SCLK

[L9]

EN_SM

Tieto:

+3.3V(AVDD2)

[H5]

AFE5804

www.ti.com ................................................................................................................................................ SBOS442A – JUNE 2008 – REVISED SEPTEMBER 2008

The AFE5804 has a set of internal registers that can be accessed through the serial interface formed by pins CS

(chip select, active low), SCLK (serial interface clock), and SDATA (serial interface data). When CS is low, the

following actions occur:

• Serial shift of bits into the device is enabled

• SDATA (serial data) is latched at every rising edge of SCLK

• SDATA is loaded into the register at every 24th SCLK rising edge

If the word length exceeds a multiple of 24 bits, the excess bits are ignored. Data can be loaded in multiples of

24-bit words within a single active CS pulse. The first eight bits form the register address and the remaining 16

bits form the register data. The interface can work with SCLK frequencies from 20MHz down to very low speeds

(a few hertz) and also with a non-50% SCLK duty cycle.

After power-up, the internal registers must be initialized to the respective default values. Initialization can be

done in one of two ways:

1. Through a hardware reset, by applying a low-going pulse on the ADS_RESET pin; or

2. Through a software reset; using the serial interface, set the S_RST bit high. Setting this bit initializes the

internal registers to the respective default values and then self-resets the bit low. In this case, the

ADS_RESET pin stays high (inactive).

Figure 90. Typical Connection Diagram for the SPI Control Lines

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