MCP6S92 datasheet(21/40 Pages) MICROCHIP

21 / 40 page

 2004 Microchip Technology Inc.

DS21908A-page 21

MCP6S91/2/3

5.0

DIGITAL FUNCTIONS

The

MCP6S91/2/3

PGAs

use

standard

SPI

compatible serial interface to receive instructions from

a controller. This interface is configured to allow daisy-

chaining with other SPI devices.

5.1

SPI Timing

Chip Select (CS) toggles low to initiate communica-

tion with these devices. The first byte of each SI word

(two bytes long) is the instruction byte, which goes

into the Instruction register. The Instruction register

points the second byte to its destination. In a typical

application, CS is raised after one word (16 bits) to

implement the desired changes. Section 5.3 “Daisy-

Chain Configuration”, covers applications using

multiple 16-bit words. SO goes low after CS goes

high; it has a push-pull output that does not go into a

high-Z state.

The MCP6S91/2/3 devices operate in SPI modes 0,0

and 1,1. In 0,0 mode, the clock idles in the low state

(Figure 5-1). In 1,1 mode, the clock idles in the high

state (Figure 5-2). In both modes, SI data is loaded into

the PGA on the rising edge of SCK, while SO data is

clocked out on the falling edge of SCK. In 0,0 mode, the

falling edge of CS also acts as the first falling edge of

SCK (see Figure 5-1). There must be multiples of 16

clocks (SCK) while CS is low or commands will abort

(see Section 5.3 “Daisy-Chain Configuration”).

FIGURE 5-1:

Serial Bus Sequence for the PGA; SPI™ 0,0 Mode (see Figure 1-4).

FIGURE 5-2:

Serial Bus Sequence for the PGA; SPI™ 1,1 Mode (see Figure 1-5).

SCK

Instruction Byte

Data Byte

(first 16 bits out are always zeros)

SCK

Instruction Byte

Data Byte

(first 16 bits out are always zeros)

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