MAX17823B datasheet(49/121 Pages) MAXIM

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MAX17823B

12-Channel High-Voltage Data Acquisition System

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Data Type

Description

Command byte

A byte defining the command packet type, generally either a read or a write.

A byte defining the register address to be read or written.

Data-check byte

An error and alert status byte sent and returned with all reads.

PEC byte

A Packet Error Checking byte sent and returned with every packet except HELLOALL.

Alive-counter

A byte functioning as a device counter on all reads and writes, if ALIVECNTEN = 1.

Fill byte

Bytes transmitted in READALL command packets for clocking purposes only.

Command Bytes

The Battery-Management UART Protocol supports six command types summarized in Table 22.

Table 22. Command Packet Types

Command

Description

Data-Check

PEC

Alive-

Counter

Packet Size

(Characters)

HELLOALL

Writes a unique device address to each device in

the daisy-chain. Required for system initialization.

WRITEALL

Writes a specified register in all devices.

Yes

WRITEDEVICE Writes a specified register in a single device.

Yes

READALL

Reads a specific register from all devices.

Yes

12 + (4z)

READDEVICE

Reads a specified register from a single device.

Yes

ROLLCALL

Reads the ADDRESS register for 32 devices.

Yes

138

Note: z = total number of devices, ALIVECNTEN = 1, packet size includes framing characters.

Command Byte Encoding

Command bytes encoding is described in Table 23. For READDEVICE and WRITEDEVICE commands, the device

address is encoded in the command byte. The device ignores those commands containing a device address other

than its own.

Table 23. Command Byte Encoding

Command

Byte*

HELLOALL

57h

ROLLCALL

01h

WRITEDEVICE

04h

DA[4]

DA[3]

DA[2]

DA[1]

DA[0]

WRITEALL

02h

READDEVICE

05h

DA[4]

DA[3]

DA[2]

DA[1]

DA[0]

READALL

03h

*Assumes DA[4:0] = 0x00 where DA[4:0] is the device address in the ADDRESS register.

All register addresses are single-byte quantities and are defined in the Register Map. In general, if the register or

device address in a received command is not a valid address for the device, the device will ignore the read or write

and simply pass-through the packet to the next device.

All registers are 16-bit words (two data bytes) and are defined in the Register Map.

Data-Check Byte

The host uses the returned data-check byte to promptly determine if any communication errors occurred during the

packet transmission and to check if alert flags are set in any devices as shown in Table 24. The data-check byte is

returned by the READALL and READDEVICE commands. For READDEVICE, the data-check byte is updated only

by the addressed device.

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