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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 OR'd 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 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→ you 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
The return packet should be
[0] 0x21
[1] 0xA0
[2] 0x02
[3] 0x05
[4] 0xAA
[5] 0x55
assuming that the values we wrote above starting at Register 5 were actually written to the device.
USB-MODEVM Communications Protocol32 SLAU201 – November 2006
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