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USB-MODEVMProtocol
Ifthecommandissentwithnoproblem,thereturningbyte[0]isthesameasthesentonelogicallyORed
with0x20-intheprecedingfirstexample,thereturningpacketis:
[0]0x31
[1]0xA0
[2]0x02
[3]0x05
[4]0xAA
[5]0x55
Ifforsomereasontheinterfacefails(forexample,theI
2
Cdevicedoesnotacknowledge),itcomesback
as:
[0]0x51-->interface|INTF_ERROR
[1]0xA0
[2]0x02
[3]0x05
[4]0xAA
[5]0x55
Iftherequestismalformed,thatis,theinterfacebyte(byte[0])takesonavaluewhichisnotaspreciously
described,thereturnpacketis:
[0]0x93-->theusersent0x13,whichisnotvalid,so0x93returned
[1]0xA0
[2]0x02
[3]0x05
[4]0xAA
[5]0x55
Theprecedingexamplesusedwrites.Readingissimilar:
Readtwobytesfromdevicestartingatregister5ofanI
2
CdevicewithaddressA0:
[0]0x01
[1]0xA0
[2]0x02
[3]0x05
Thereturnpacketis:
[0]0x21
[1]0xA0
[2]0x02
[3]0x05
[4]0xAA
[5]0x55
assumingthattheprecedingvaluesstartingatRegister5wereactuallywrittentothedevice.
SLAU286–June2009USB-MODEVMProtocol47
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