LTC6802-1 datasheet(21/38 Pages) LINER

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LTC6802-1

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APPLICATIONS INFORMATION

Network Layer

Broadcast Commands: A broadcast command is one to

which all devices on the bus will respond. See the Bus

Protocols and Commands sections.

In daisy chained configurations, all devices in the chain

receive the command bytes simultaneously. For example,

to initiate A/D conversions in a stack of devices, a single

STCVAD command byte is sent, and all devices will start

conversions at the same time. For read and write com-

mands, a single command byte is sent, and then the stacked

devices effectively turn into a cascaded shift register, in

which data is shifted through each device to the next higher

(on a write) or the next lower (on a read) device in the

stack. See the Serial Command Examples section.

PEC Byte: The Packet Error Code (PEC) byte is a CRC

value calculated for all of the bits in a register group in

the order they are read, using the following characteristic

polynomial:

x8 + x2 + x + 1

On a read command, after sending the last byte of a register

group, the device will shift out the calculated PEC, MSB

first. For daisy-chained devices, after the PEC is read from

the first device, the data from any daisy-chained devices

will follow in the same order. For example, when read-

ing the flag registers from two stacked devices (bottom

device A and top device B), the data will be output in the

following order:

FLGR0(A), FLGR1(A), FLGR2(A), PEC(A), FLGR0(B),

FLGR1(B), FLGR2(B), PEC(B)

Toggle Polling: Toggle polling allows a robust determina-

tion both of device states and of the integrity of the con-

nections between the devices in a stack. Toggle polling

is enabled when the LVLPL bit is low. After entering a

polling command, the data out line will be driven by the

slave devices based on their status. When polling for the

A/D converter status, data out will be low when any device

is busy performing an A/D conversion and will toggle at

1kHz when no device is busy. Similarly, when polling for

interrupt status, the output will be low when any device

has an interrupt condition and will toggle at 1kHz when

none has an interrupt condition.

Toggle Polling—Daisy-Chained Broadcast Polling: The

SDO pin (bottom device) or SDI pin (stacked devices) will

be low if a device is busy/in interrupt. If it is not busy/not

in interrupt, the device will pass the signal from the SDOI

input to data out (if not the top-of-stack device) or toggle

the data out line at 1kHz (if the top-of-stack device).

The master pulls CSBI high to exit polling.

Level polling: Level polling is enabled when the LVLPL

bit is high. After entering a polling command, the data

out line will be driven by the slave devices based on their

status. When polling for the A/D converter status, data

Figure 10. Transmission Format (Poll)

CSBI

SCKI

SDI

SDO

POLL STATE

MSB (CMD)

BIT6 (CMD)

LSB (CMD)

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