MCP6S92 Microchip Technology Inc., MCP6S92 Datasheet - Page 25

• Manufacturer Part Number: MCP6S92
• Description: Single-ended, Rail-to-rail I/o, Low-gain Pga
• Manufacturer: Microchip Technology Inc.

5.2.5
The software shutdown command allows the user to
put the amplifier into a low-power mode (see
Register 5-1). In this Shutdown mode, most pins are
high-impedance (Section 4.5 “Shutdown Mode” and
Section 5.1 “SPI Timing” cover the exceptions at pins
V
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
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
FIGURE 5-3:
 2004 Microchip Technology Inc.
REF,
4. Clock out the instruction and data
5. Device 1 automatically shifts data
6. Raise CS.
1. Set CS low.
2. Clock out the instruction and data
3. Device 1 automatically clocks out all
V
for Device 1 (16 clocks) to Device 1.
from Device 1 to Device 2 (16 clocks).
OUT
for device 2 (16 clocks) to Device 1.
zeros (first 16 clocks) to Device 2.
Daisy-Chain Configuration
SHUTDOWN COMMAND
and SO).
PICmicro
Microcontroller
®
microcontroller I/O pins.
Daisy-Chain Configuration.
®
SCK
SO
CS
CS
SCK
SI
Device 1
SO
00100000 00000000
01000001 00000111
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.
Device 1
Device 1
CS
SCK
SI
Device 2
SO
MCP6S91/2/3
00000000 00000000
00100000 00000000
Device 2
Device 2
DS21908A-page 25