Datasheet

 2014 Microchip Technology Inc. DS20005292A-page 37

MCP2221

3.1.3.1 Responses

TABLE 3-16: SUB-COMMAND STRUCTURE – WRITE USB SERIAL NUMBER DESCRIPTOR

STRING SUB-COMMAND

Byte Index Value Effect

0 0xB1 Write Flash Data – command code

1 0x04 Write USB Serial Number Descriptor String – writes the USB Serial

Number String Descriptor used during the USB enumeration

(2)

Number of bytes + 2 in the provided USB Serial Number Descriptor

String. The actual String starts at Byte Index 4

3 0x03 The value at this index must always be 0x03.

4 + 2 x Unicode_char_number + 0

(1)

Lower byte of the 16-bit Unicode character

4 + 2 x Unicode_char_number + 1

(1)

Higher byte of the 16-bit Unicode character

Note 1: “Unicode_char_number” value starts from 0 to a maximum of 30 (included).

2: The value at Byte Index 2 must be 2 + 2 x (number of Unicode characters in the string).

TABLE 3-17: RESPONSE STRUCTURE – READ CHIP FACTORY SERIAL NUMBER SUB-

COMMAND

Byte

Index

Value Effect

0 0xB1 Write Flash Data – command code

1 0x00 Command completed successfully

0x02 Command not supported

0x03 Command not allowed

2-63 Don’t care