Datasheet

 2014 Microchip Technology Inc. DS20005292A-page 31
MCP2221
TABLE 3-9: RESPONSE STRUCTURE – READ USB SERIAL NUMBER DESCRIPTOR STRING
SUB-COMMAND
Byte Index Value Effect
0 0xB0 Read Flash Data – command code echo
1 0x00 Command completed successfully
2
(2)
The 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
(4 + 2 x Unicode_char_number + 2) - 63
(1)
Don’t care.
Only if the USB string descriptor is less than 60-bytes long in
total.
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 3-10: RESPONSE STRUCTURE – READ CHIP FACTORY SERIAL NUMBER
SUB-COMMAND
(1)
Byte Index Value Effect
0 0xB0 Read Flash Data – command code echo
1 0x00 Command completed successfully
2 Structure length
3Don’t
care
4 - (4 + Structure length - 1) Structure data – Factory Serial Number String
(4 + Structure length) - 63 Don’t
care
Note 1: The Chip Serial Number is typically 8 bytes in length.