MAX17843ACBV datasheet(96/131 Pages) MAXIM

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UART Optical Isolation

The daisy-chain may use optical isolation instead of trans-

former or capacitor isolation (see Figure 68).

Device Initialization Sequence

Immediately after reset, all device addresses are set to

0x00 and the UART baud rate and receive modes have not

been autodetected; therefore, the following initialization

sequence is recommended after every reset or after any

change to the hardware configuration for differential mode:

After the daisy-chain is initialized, each device should be

configured for operation as follows:

1) Perform a READALL of the status registers:

The ALRTRST bit should be set in all devices to

signify a reset occurred.

Check for other unexpected alerts.

2) Clear the ALRTRST bit on each device so that future

unintended resets can be detected.

3) Change configuration registers as necessary with

WRITEALL commands:

Configure the alert enables and alert thresholds

required by the application.

Configure the acquisition mode.

4) Perform all necessary key-on diagnostics.

5) Start the acquisition cycle.

6) Continuously monitor diagnostic and alert status bits.

7) Periodically perform additional diagnostics, as

required by the application.

Error Checking

Data integrity is provided by Manchester encoding, par-

ity, character framing, and packet-error checking (PEC).

The combination of these features verify stage-to-stage

communication both in the write and read directions, with

a hamming distance (HD) value of 6 for commands with

a length up to 247 bits (counted prior to Manchester-

encoding and character framing. This is equivalent to the

longest possible command packet for a daisy-chain of

up to 13 devices. The data-check byte is present in the

READALL and READDEVICE commands to verify that

the entire command propagated without errors. Using the

data-check and PEC bytes, complete transaction integrity

for READALL and READDEVICE command packets can

be verified.

PEC Errors

If the device receiver receives an invalid PEC byte, the

ALRTPEC bit is set in the STATUS register. A device does

not execute any write command unless the received PEC

matches the calculated PEC so to verify the write com-

mand execution, the host should perform a READALL to

verify the contents of the written register.

For returned read packets, the host should store the

received data, perform the PEC calculation, and compare

the results to the received PEC byte before considering the

data to be valid. To support PEC, the host must implement

an 8-bit cyclic redundancy check (CRC-8) encoding and

decoding algorithm based on the following polynomial:

P(x) = x8 + x6 + x3 + x2 + 1

Figure 68. UART Optical Isolation

RXLP

CFILTER

15pF

RFILTER

1.5kΩ

VAA

FROM UART

DATA SOURCE

ACPL-M72T

3.3V

TO UART

DATA SOURCE

ACPL-M72T

ROPTO

RXLN

GNDL

TXLN

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

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