AFE4490 datasheet(40/69 Pages) TI

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SPISTE

SPISIMO

SCLK

'RQ¶W FDUH, can be high or low.

D23

D22

D17

D16

D15

D14

SPISOMI

AFE4400

SBAS601D – DECEMBER 2012 – REVISED MAY 2013

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Reading Data

The AFE4400 includes a mode where the contents of the internal registers can be read back on the SPISOMI

pin. This mode may be useful as a diagnostic check to verify the serial interface communication between the

external controller and the AFE. To enable this mode, first set the SPI_READ register bit using the SPI write

command, as described in the Writing Data section. In the next command, specify the SPI register address with

the desired content to be read. Within the same SPI command sequence, the AFE outputs the contents of the

specified register on the SPISOMI pin. Figure 54 shows a timing diagram for the SPI read operation.

(1) The SPI_READ register bit must be enabled before attempting a serial readout from the AFE.

(2) Specify the register address of the content that must be readback on bits A[7:0].

(3) The AFE outputs the contents of the specified register on the SPISOMI pin.

Figure 54. AFE SPI Read Timing Diagram

After power-up, the internal registers must be initialized to the default values. This initialization can be done in

one of two ways:

•

Through a hardware reset by applying a low-going pulse on the RESET pin, or

•

By applying a software reset. Using the serial interface, set SW_RESET (bit D3 in register 00h) high. This

setting initializes the internal registers to the default values and then self-resets to '0'. In this case, the RESET

pin is kept high (inactive).

AFE SPI Interface Design Considerations

Note that when the AFE4400 is deselected, the SPISOMI, CLKOUT, ADC_RDY, PD_ALM, LED_ALM, and

DIAG_END digital output pins do not enter a 3-state mode. This condition, therefore, must be taken into account

when connecting multiple devices to the SPI port and for power-management considerations.

AFE REGISTER MAP

The AFE consists of a set of registers that can be used to configure it, such as receiver timings, I-V amplifier

settings, transmit LED currents, and so forth. The registers and their contents are listed in Table 4. These

registers can be accessed using the AFE SPI interface.

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