MCP6S21 datasheet(19/43 Pages) MICROCHIP

19 / 43 page

 2003 Microchip Technology Inc.

DS21117A-page 19

MCP6S21/2/6/8

5.2

Registers

The analog functions are programmed through the SPI

interface using 16-bit words (see Figure 5-1 and

Figure 5-2). This data is sent to two of three 8-bit regis-

ters: Instruction Register (Register 5-1), Gain Register

(Register 5-2) and Channel Register (Register 5-3).

The power-up defaults for these three registers are:

• Instruction Register: 000x xxx0

• Gain Register: xxxx x000

• Channel Register: xxxx x000

Thus, these devices are initially programmed with the

Instruction Register set for NOP (no operation), a gain

of +1 V/V and CH0 as the input channel.

5.2.1

INSTRUCTION REGISTER

The Instruction Register has 3 command bits and 1

indirect address bit; see Register 5-1. The command

bits include a NOP (000) to support daisy chaining (see

Section 5.3, “Registers”); the other NOP commands

shown should not be used (they are reserved for future

use). The device is brought out of Shutdown mode

when a valid command, other than NOP or Shutdown, is

sent and CS is raised.

INSTRUCTION REGISTER

W-0

U-x

W-0

—

—A0

bit 7

bit 0

bit 7-5

M2-M0: Command Bits

000

= NOP (Default) (Note 1)

001

= PGA enters Shutdown Mode as soon as a full 16-bit word is sent and CS is raised.

(Notes 1 and 2)

010

= Write to register.

011

= NOP (reserved for future use) (Note 1)

1XX

= NOP (reserved for future use) (Note 1)

bit 4-1

Unimplemented: Read as ‘0’ (reserved for future use)

bit 0

A0: Indirect Address Bit

= Addresses the Channel Register

= Addresses the Gain Register (Default)

Note 1: All other bits in the 16-bit word (including A0) are “don’t cares”.

2: The device exits Shutdown mode when a valid command (other than NOP or Shut-

down) is sent and CS is raised; that valid command will be executed. Shutdown

does not toggle.

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

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