PS810 datasheet(26/46 Pages) MICROCHIP

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PS810

DS21904C-page 26

8.2

SPS Single Pin Serial Battery

Data Interface

The PS810 can also communicate using one pin, the

SDA pin with the Single Pin Serial protocol (SPS). The

single

serial

interface

communication

asynchronous

return-to-one

protocol.

The

signal

requires an external pull-up resistor. The timing of the

driven low pulses defines the communication.

A Break cycle starts a command from the host to the

battery. The command is eight bits long. After this, eight

data bits are either sent to the battery or received from

the battery. The Least Significant bits are sent first.

The Break cycle is defined by a low period for a time

equal to or greater than tB, then returned high for a time

greater than or equal to tBR.

The data bits consist of three sections each:

Start: a logic low for at least time tSTR.

Data: data high or low valid by time tDS and held

until time tDH/V.

Stop: logic high by time tSSU and held until time

TCYC.

The SPS protocol only allows one byte to be read per

command code. Thus, commands that receive two-

byte pieces of data must be executed one byte at a

time. To get a two-byte data, the command code for the

high byte must be sent, the high data byte received and

then, the command code for the low data byte must be

sent to receive the low data byte.

Furthermore, it is possible that the piece of data has

changed in between the time it took to get the high byte

and the low byte if the host system is communicating

slowly. Therefore, it is recommended to always verify

the data hasn’t changed. This is done by reading the

high byte, then reading the low byte, then rereading the

high byte and comparing it to the first read to make sure

it is the same. If it is not the same, then the low byte can

be reread and matched with the new high byte.

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