MCP2221 datasheet(23/80 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS20005292B-page 23

MCP2221

3.0

USB HID COMMUNICATION

Except for the USB CDC and UART modules, all the

other modules in the MCP2221 use USB HID protocol

for communication.

The USB HID protocol uses 64-byte reports.

A typical command exchange starts with a 64-byte

packet that is written by the USB Host (i.e., the PC).

Afterward, the USB Host reads the response from the

device as a 64-byte packet.

3.1

USB HID Commands/Responses

3.1.1

STATUS/SET PARAMETERS

This command offers many options for this device. It is

used to poll for the status of the device. It is also used

to establish certain I2C bus parameters/conditions.

TABLE 3-1:

COMMAND STRUCTURE

Byte

Index

Function Description

Value

Effect

0x10

Status/Set Parameters – command code

Don’t care

Any value

Cancel current I2C/SMBus

transfer (sub-command)

0x10

When this value is put in this field, the device will cancel the

current I2C/SMBus transfer and will attempt to free the I2C bus.

This command is very useful since it can cancel a transfer and

free the bus. An example would be when trying to communicate

with a device using a wrong address. This will cause a timeout

to occur. This timeout situation can be read using the

“Status/Set Parameter” and the cancellation of the I2C/SMBus

transfer can be achieved by this sub-command.

Any other

value

No effect.

3Set I2C/SMBus communication

speed (sub-command)

0x20

When this value is put in this field, the device will take the next

command field and interpret it as the system clock divider that

will give the I2C/SMBus communication clock.

Any other

value

No effect.

4The I2C/SMBus system clock

divider that will be used to

establish the communication

speed

The value in this field is being taken into consideration only

when the Byte Index 3 contains the code for establishing a new

communication speed. In all the other cases, this field’s value

won’t matter.

5-63

Don’t care

Any value

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