AFE8221RFP datasheet(13/48 Pages) TI

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CONTROL INTERFACE

SPI Interface

SCK

MOSI

MISO

INSTRUCTI N

DATA

REG_ADDR

MEM

MEM_ADDR

AFE8221

SBAS394A – APRIL 2007 – REVISED MARCH 2008

The second 16 bits are the data transfer, which is

input on MOSI for a write cycle or output on MISO for

Configuration and control data are written to the

a read cycle.

AFE8221 via the control interface. The control

interface supports two protocols, SPI and I2C. If the

Figure 5 shows an SPI write cycle. The cycle is

CTRL_MODE pin is tied low, then an SPI interface is

initiated by the high-to-low transition of the CS line.

implemented. If CTRL_MODE is tied high, then an

32 SCK pulses clock the instruction and the data into

I2C protocol-compatible interface is implemented.

the MOSI line. Data are clocked in MSB first. The first

16 bits are the instruction. There are two possible

write cycle instructions: register write and memory

write. The formats for these instructions are shown in

The SPI interface consists of four signals: a serial

Figure 6 and Figure 7, respectively.

clock (SCK), an active-low chip select (CS), a serial

data input (MOSI—master out, slave in), and a serial

The only information required for a register write is

data output (MISO—master in, slave out). Data are

the seven-bit register address (REG_ADDR). For a

transferred in groups of 32 bits. The first 16 bits are

memory write, both the five-bit memory select (MEM)

the instruction, which indicates:

plus the six-bit memory address (MEM_ADDR) are

required.

1. If data are to be written or to be read;

2. If the data target is a register or RAM; and

Following the 16-bit instruction, the 16-bit data word

is clocked in, again MSB first. At the end of the write

3. The address of the data target.

cycle, this data word is written to the appropriate

NOTE: To terminate a Write/Read cycle, CS must be brought high.

Figure 5. SPI Control Interface Write Cycle

Figure 6. Register Write Instruction Format

Figure 7. Memory Write Instruction Format

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