MCP6S92 datasheet(25/40 Pages) MICROCHIP

25 / 40 page

 2004 Microchip Technology Inc.

DS21908A-page 25

MCP6S91/2/3

5.2.5

SHUTDOWN COMMAND

The software shutdown command allows the user to

put the amplifier into a low-power mode (see

high-impedance (Section 4.5 “Shutdown Mode” and

Section 5.1 “SPI Timing” cover the exceptions at pins

VREF, VOUT and SO).

Once the PGA has entered Shutdown mode, it will

remain in this mode until either a valid command is sent

to the device (other than NOP or Shutdown) or the

device is powered down and back up again. The

internal registers maintain their values while in

shutdown.

Once brought out of Shutdown mode, the part returns

to its previous state (see Section 5.2.1 “Ensuring

Valid Data in the Registers” for exceptions to this

rule). This makes it possible to bring the device out of

shutdown mode using one command; send a com-

mand to select the current channel (or gain) and the

device will exit shutdown with the same state that

existed before shutdown.

5.3

Daisy-Chain Configuration

Multiple MCP6S91/2/3 devices can be connected in a

daisy-chain configuration by connecting the SO pin

from one device to the SI pin on the next device and

using common SCK and CS lines (Figure 5-3). This

approach reduces PCB layout complexity and uses

fewer PICmicro® microcontroller I/O pins.

The example in Figure 5-3 shows a daisy-chain

configuration with two devices, although any number of

devices can be configured this way. The MCP6S91 and

MCP6S92 can only be used at the far end of the daisy-

chain, because they do not have a serial data out (SO)

pin. As shown in Figure 5-4 and Figure 5-5, both SI and

SO data are sent in 16-bit (2 byte) words. These

devices abort any command that is not a multiple of 16

bits.

When using the daisy-chain configuration, the maxi-

mum clock speed possible is reduced to

≈ 5.8 MHz due

to the SO pin’s propagation delay (see Electrical

Specifications).

The internal SPI shift register is automatically loaded

with zeros whenever CS goes high (a command is

executed). Thus, the first 16-bits out of the SO pin after

the CS line goes low are always zeros. This means that

the first command loaded into the next device in the

daisy-chain is a NOP. This feature makes it possible to

send shorter command and data byte strings when the

farthest devices do not need to change. For example, if

there were three devices on the chain, and only the

middle device needed changing, then only 32 bytes of

data need to be transmitted (for the first and middle

devices). The last device on the chain would receive a

NOP

when the CS pin is raised to execute the

command.

FIGURE 5-3:

Daisy-Chain Configuration.

PICmicro®

SCK

Device 1

00100000 00000000

SCK

Device 2

00000000 00000000

Device 1

01000001 00000111

Device 2

00100000 00000000

4. Clock out the instruction and data

for Device 1 (16 clocks) to Device 1.

5. Device 1 automatically shifts data

from Device 1 to Device 2 (16 clocks).

6. Raise CS.

1. Set CS low.

2. Clock out the instruction and data

for device 2 (16 clocks) to Device 1.

3. Device 1 automatically clocks out all

zeros (first 16 clocks) to Device 2.

Microcontroller

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