MXT1664T3-ABESSQTP datasheet(37/98 Pages) MICROCHIP

37 / 98 page

MXT1664T3 2.0

 2018 Microchip Technology Inc.

DS40002054A-page 37

FIGURE 8-5:

CONTINUOUS MESSAGE READ EXAMPLE – I2C CHECKSUM MODE

There are no checksums added on any other I2C reads. An 8-bit CRC can be added, however, to all I2C writes, as

described in Section 8.3 “I2C Writes in Checksum Mode”.

An alternative method of reading messages using the CHG line is given in Section 8.6 “CHG Line”.

8.6

CHG Line

The CHG line is an active-low, open-drain output that is used to alert the host that a new message is available in the

Message Processor T5 object. This provides the host with an interrupt-style interface with the potential for fast response

times. It reduces the need for wasteful I2C communications.

The CHG line should always be configured as an input on the host during normal usage. This is particularly important

after power-up or reset (see Section 5.0 “Power-up / Reset Requirements”).

A pull-up resistor is required to VddIO (see Section 2.0 “Schematics”).

The CHG line operates in two modes when it is used with I2C communications, as defined by the Communications

Configuration T18 object.

Report ID

Data

Checksum

Report ID

Data

Checksum

Start Address of

Message Count Object

Set Address Pointer

Read Message Count

START

SLA+R

Count = 3

Message Count Object

Read Message Data

Message Processor Object – Message # 1

size bytes

Message Processor Object – Message # 2

Message Processor Object – Message # 3

STOP

Continuous

Read

START

SLA+W

LSB

MSB | 0x80

Checksum

STOP

Report ID

Data

Checksum

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