MCP8026 datasheet(38/64 Pages) MICROCHIP

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MCP8025/6

DS20005339B-page 38

 2016 Microchip Technology Inc.

FIGURE 4-4:

DE2 Packet Format.

FIGURE 4-5:

DE2 Packet Timing.

4.5.4

MESSAGING INTERFACE

A command byte will always have the most significant

bit 7 (MSb) set to ‘1’. Bits 6 and 5 are reserved for future

use and should be set to ‘0’. Bits 4–0 are used for

commands. That allows for 32 possible commands.

4.5.4.1

Host to MCP8025/6

Messages sent from the host to the MCP8025/6

devices consist of either one or two eight-bit bytes. The

first byte transmitted is the command byte. The second

byte transmitted, if required, is the data for the

command.

If a multi-byte command is sent to the MCP8025/6

devices and no second byte is received by the

MCP8025/6 devices, then a ‘Not Acknowledged’

(NACK) message will be sent back to the host after a

5 ms time-out period.

4.5.4.2

MCP8025/6 to Host

A solicited response byte from the MCP8025/6 devices

will always echo the command byte with bit 7 set to ‘0’

(Response) and with bit 6 set to ‘1’ for ‘Acknowledged’

(ACK) or ‘0’ for ‘Not Acknowledged’ (NACK). The

second byte, if required, will be the data for the host

command. Any command that causes an error or is not

supported will receive a NACK response.

The MCP8025/6 devices may send unsolicited

command messages to the host controller. No

message to the host controller requires a response

from the host controller.

STOP

START

DE2

Message Format

STOP

START

TSTART = 1.5T – uncertainty on start

Detection (worse case: 2x TS)

TS = T/16 (oversampled bit-cell period)

Receiver samples the incoming data

using x16 baud rate clock

Sample incoming data

at the bit-cell center

TSTART

T = 1/Baud Rate (bit-cell period)

Detect start bit by sensing

transition from logic 1 to logic 0

worst

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