MAX17841B datasheet(22/33 Pages) MAXIM

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Error Checking

Itishighlyrecommendedthatthehostutilizethevarious

error checking features available in both the ASCI and the

battery management UART protocol to ensure the integ-

rity of the data being received. The host should implement

the following verifications:

● Verification of write data received (matching values,

number of bytes)

● Verification of read data received (allowed values,

ranges, number of bytes)

● Verification of the received PEC, data-check, and

alive-counter bytes

● VerificationofASCIFMEAregister

● Verification of the ASCI status bits (RX_Error_

Status, RX_Overflow_Status, TX_Overflow_Status,

POR_Flag)

Corrupted Preamble Character

If the preamble for a message is corrupted, none of the

message is entered into the receive buffer. To detect

this failure mode, the host should always verify that any

message that it transmitted was also received into the

receive buffer. In the case where the host is polling a

identify each message sent by sending up to 256 different

seed values for the alive-counter byte. The host should

increment the seed value every time a message is sent

by the host so that its propagation through the daisy chain

can be verified in the received data. The alive-counter

byteissentafterthePECbyteandthereforethePECis

not affected.

Corrupted Message Content

Manchester, parity, and PEC errors are indications that

the data in the message may have been corrupted. For

each UART message received, the host should perform

the appropriate computations on any error-checking bytes

that may be available in the received message:

● Data-Check byte: Error status provided by the slave

device(s);sentandreturnedonreadsofslavedevice

data as described in the slave device data sheet.

● PECbyte:CRC-8packeterror-checkingbyteprovided

by the slave device(s); sent and returned with every

message as described in the slave device data sheet.

● Alive-Counter byte: Used to verify the number of

devicesrespondingtoatransmittedmessage;canbe

sent and received with every message as described in

the slave device data sheet.

Table 11. Transaction Sequence for UART Write and Read (continued)

SPI DIN

SPI DOUT

DESCRIPTION

TRANSACTION 9

Readthereceivebufferandverifythatthedeviceregisterdataiswhatwaswrittenduringthe

WRITEALLsequence

93h

xxh

RD_NXT_MSGSPIcommandbyte

xxh

03h

Sentcommandbyte(READALL)

xxh

12h

Sent register address

xxh

B1h

LSbyteofdevice1

xxh

B2h

MS byte of device 1

xxh

B1h

LSbyteofdevice0

xxh

B2h

MS byte of device 0

xxh

00h

Data-checkbyte(=00hifallstatusbitshavebeencleared)

xxh

67h

PEC(fortheprevious7bytes)

xxh

02h

Alive-counterbyte(=sentseed+2,ifalivecounterisenabled)

TRANSACTION 10

Checkforreceivebuffererrors

09h

xxh

ReadRX_Interrupt_Flagsregister

xxh

00h

Ifnoerrors,continue.Otherwise,clearandgotoerrorroutine.

Maxim Integrated │ 22

MAX17841B

Automotive SPI Communication Interface (ASCI)

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