Table 6. UART Operational Modes

MODE

DESCRIPTION

Shutdown

Asserting SHDNresetsallASCIregistersandbufferdatatotheirdefaultstate,stopssendingandreceiving

UARTcommunication,anddisablesthe3.3Vregulator.

Transmit

Preambles

Transmitspreamblescontinuously(noidlestate).UsedtowakeuptheUARTslavedevicesandinitializethe

UART baud rate of each slave device. This mode takes precedence over all transmit modes except Transmit

Pause mode.

Keep-Alive

Periodically sends a stop character to prevent UART slave devices from shutting down during periods of no

communication(idlestate).Theidletimeinbetweentheperiodicstopcharactersisprogrammablefromzero

to10.24msthroughtheKeep-Alive[3:0]configuration.Thedefaultsettingisinfinite(modedisabled).The

TransmitPause,TransmitPreambles,andtheTransmitQueuemodestakeprecedenceoverthismode.

TransmitQueue

(default mode)

Startstransmissionofthemessageloadedinthetransmitqueueif1)thereissufficientspaceinthereceive

bufferforthemessage(RX_Full_Statusisfalse)or2)thelimitationsonmessagelengthareremoved

(TX_Unlimitedisset).Defaultisenabled.

Transmit Unlimited

In this mode, the transmit queue automatically limits the message length to 255 bytes instead of the default

62-byte limit, and the message transmission is permitted even if the message length is greater than the

availablewritespaceinthereceivebuffer.

Transmit Pause

PlacesthetransmitterintoidlestateoncetheUARThasfinishedtransmittingthecurrentbyte,however,the

TX_Busy_StatusandTX_Idle_Statusbitsremainunchanged.Transmissionresumeswhenthisbitiscleared.

This mode takes precedence over all other transmit modes.

TransmitOdd

Parity

Transmits characters with odd parity. Since the battery management UART protocol uses even parity, this

modecanbeusedtotestthesystem’sabilitytodetectparityerrors.Evenparityisdefault.

TransmitNoStop

Transmitsmessageswithoutastopcharacter.BysendingsubsequentmessageswiththeNoPreamblebit,

aframedmessageofindefinitelengthcanbeconstructed.TheTX_Unlimitedbitmustbesetformessages

greater than 62 bytes.

TransmitNo

Preamble

Transmitsmessageswithoutapreamble.ByfirstsendingamessageinwhichtheTX_No_Stopbitisset,and

thensendingmessageswiththisbitset,aframedmessageofindefinitelengthcanbeconstructed.However,

if the preceding message was terminated with a stop character (end of frame), then the data sent in this

modeisunframed(withoutpreamble)andisnotstoredinthereceivebuffer.

TransmitRawData DisablesManchesterencodingoftransmitteddata.Inthismode,eachdatabyteistransmittedasone

character (instead of two characters).

ReceiveRawData

DisablesManchesterdecodingofthereceiveddata.Inthismode,thereisonedatabytestoredforevery

character received (instead of every two received).

Maxim Integrated │ 14

MAX17841B

Automotive SPI Communication Interface (ASCI)

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