Data Types

Maxim’s battery management UART protocol supports

several different data types as described in Table3. The

ASCI does not interpret the significance of any of these

data types. It is up to the host to both compose the data

being transmitted and interpret the data being received.

For example, the host must compute the proper PEC

value for each transmitted message and must verify the

PECvalueoneachreceivedmessage.

Assigning Slave Device Addresses

The battery management UART protocol requires that the

host assign a unique and contiguous address between 0

and31toeachUARTslavedevicesothatthehostcan

address each slave device individually as desired. The host

performs this assignment by specifying a seed address

intheHELLOALLcommandsequence.Asthecommand

propagates up the daisy-chain, each slave device assigns

itsownaddress.TheHELLOALLsequencereturnsavalue

from which the host can determine the number of devices

in the daisy-chain as well as the device addresses.

Table 3. Message Data Types

Table 4. Common Commands

DATA TYPE

DESCRIPTION

Command

Definesthetypeofmessage,eitherawritecommandorareadcommand.

Address

Register address to be read or written.

Data

Register data being read or written.

PEC

CRC-8packeterror-checkingbyte;sentandreturnedwitheverymessage.

Data-Check

Errorstatusprovidedbytheslavedevices;returnedonlyonreads.

Alive-Counter

Used to verify the number of devices responding to a transmitted message. This byte is optional but is

recommended for error-checking purposes.

Fill

ByteswithvaluesC2horD3htransmittedasapartofreadcommandssothatthetotalnumberofbytessent

equalsthenumberofbytesreceived.However,thesebytesarenotreturnedtoreceiverwiththeiroriginal

values;insteadeachslavedevicereplacesthefillbyteswiththeregisterdatabeingrequestedbythehost.

COMMAND BYTE

VALUE

DESCRIPTION

HELLOALL

57h

Assigns a unique device address to each device in the daisy-chain.

WRITEALL

02h

Writesaspecificregisterinalldevices.

READALL

03h

Readsaspecificregisterfromalldevices.

Maxim Integrated │ 12

MAX17841B

Automotive SPI Communication Interface (ASCI)

www.maximintegrated.com