AFE4490 datasheet(39/69 Pages) TI

39 / 69 page

D23

D22

D17

D16

D15

D14

SPISTE

SPISIMO

SCLK

'RQ¶W FDUH, can be high or low.

AFE4400

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SBAS601D – DECEMBER 2012 – REVISED MAY 2013

SERIAL PROGRAMMING INTERFACE

The SPI-compatible serial interface consists of four signals: SCLK (serial clock), SPISOMI (serial interface data

output), SPISIMO (serial interface data input), and SPISTE (serial interface enable).

The serial clock (SCLK) is the serial peripheral interface (SPI) serial clock. SCLK shifts in commands and shifts

out data from the device. SCLK features a Schmitt-triggered input and clocks data out on the SPISOMI. Data are

clocked in on the SPISIMO pin. Even though the input has hysteresis, TI recommends keeping SCLK as clean

as possible to prevent glitches from accidentally shifting the data. When the serial interface is idle, hold SCLK

low.

The SPI serial out master in (SPISOMI) pin is used with SCLK to clock out the AFE4400 data. The SPI serial in

master out (SPISIMO) pin is used with SCLK to clock in data to the AFE4400. The SPI serial interface enable

(SPISTE) pin enables the serial interface to clock data on the SPISIMO pin in to the device.

READING AND WRITING DATA

The device has a set of internal registers that can be accessed by the serial programming interface formed by

the SPISTE, SCLK, SPISIMO, and SPISOMI pins.

Writing Data

When SPISTE is low,

•

Serially shifting bits into the device is enabled.

•

Serial data (on the SPISIMO pin) are latched at every SCLK rising edge.

•

The serial data are loaded into the register at every 32nd SCLK rising edge.

In case the word length exceeds a multiple of 32 bits, the excess bits are ignored. Data can be loaded in

multiples of 32-bit words within a single active SPISTE pulse. The first eight bits form the register address and

the remaining 24 bits form the register data. Figure 53 shows a diagram of the write timing.

Figure 53. AFE SPI Write Timing Diagram

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