MAX17841B datasheet(9/33 Pages) MAXIM

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nate the transaction (single-byte transaction), continue to

clock data out (write transaction), or start clocking data in

(readtransaction).However,itdoesnotsendandreceive

data at the same time (half-duplex operation).

For register transactions, the host first sends a single-byte

(odd addresses) or write-only (even addresses). For a

read transaction, the second byte is the read data sent by

the ASCI to the host. For a write transaction, the second

byte is the write data sent by the host to the ASCI. Multiple

data bytes are allowed as long as CS remains active-

low—the ASCI automatically selects the next read-only

(for writes). The SPI transaction is terminated when the

host drives CS high.

Buffer Transactions

Buffer transactions can consist of only a command byte,

a command byte followed by one or more read bytes, or

a command byte followed by one or more write bytes. All

allowed transactions are specified in Table 9.

SPI Timing

TheASCIisonlycompatiblewithSPImode0(CPOL=

0/CPHA=0).Inthismode,dataisalwaysdrivenonthe

fallingedgeofSCLKandisalwayssampledontherising

edgeofSCLK.

Forreads,theASCIstartsdrivingDOUTonthefirstfall-

ing edge of SCLK immediately after theASCI samples

the least-significant bit (LSB) of the command/address

byte.DINisa“don’tcare”whilereading.Readsattempted

beyondtheaddressspacereturnzero.

For writes, registers are written on the falling edge of

SCLK,afterthelastbitissampled.However,ifCS goes

highbeforethelastbit’sfallingedgeofSCLK,thatregister

is not written.

UART Interface

Slave devices that use Maxim’s battery management

UART protocol can be connected in daisy-chain fashion to

manage a multiple battery-cell stack. In a BMS, or Battery

Management System, the BMS controller is the host for

all slave devices and initiates all communication. The data

flow always starts from the host, goes up the daisy-chain

and back down to the host as represented in Figure 6.

Table 2. SPI Communication Summary

Figure 6. System Data Flow

PARAMETER

VALUE

Communication Mode

Half-duplex

Maximum Clock Frequency

4MHz

BitOrder

Most-significantbitfirst

ClockPolarity(CPOL)

0 (leading clock edge is

rising edge)

ClockPhase(CPHA)

0 (data sampled on leading

clock edge)

CHOOSE

INTERNAL OR

EXTERNAL

LOOPBACK

RXUP RXUN

TXUP TXUN

TXLP TXLN

RXLP RXLN

DEVICE (n)

RXUP RXUN

TXUP TXUN

TXLP TXLN

RXLP RXLN

DEVICE (n-1)

RXUP RXUN

TXUP TXUN

TXLP TXLN

RXLP RXLN

DEVICE 1

BMS

ISOLATION

MAX17841B

µC

BATTERY

PACK n

BATTERY

PACK (n - 1)

BATTERY

PACK 1

OPTIONAL

SERVICE

DISCONNECT

Maxim Integrated │ 9

MAX17841B

Automotive SPI Communication Interface (ASCI)

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