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USB-MODEVM Protocol
If the command is sent with no problem, the returning byte [0] should be the same as the sent one
logically ORed with 0x20 - in our first example above, the returning packet should be:
[0]
0x31
[1]
0xA0
[2]
0x02
[3]
0x05
[4]
0xAA
[5]
0x55
If for some reason the interface fails (for example, the I
2
C device does not acknowledge), it would come
back as:
[0]
0x51
--> interface | INTF_ERROR
[1]
0xA0
[2]
0x02
[3]
0x05
[4]
0xAA
[5]
0x55
If the request is malformed, that is, the interface byte (byte [0]) takes on a value which is not described
above, the return packet would be:
[0]
0x93
--> the user sent 0x13, which is not valid, so 0x93 returned
[1]
0xA0
[2]
0x02
[3]
0x05
[4]
0xAA
[5]
0x55
Examples above used writes. Reading is similar:
Read two bytes from device starting at register 5 of an I
2
C device with address A0:
[0]
0x01
[1]
0xA0
[2]
0x02
[3]
0x05
SLAU218 – August 2007
USB-MODEVM Protocol
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