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USB-MODEVM Protocol
If the command is sent with no problem, the returning byte [0] is the same as the sent one logically ORedwith 0x20 - in the preceding first example, the returning packet is:[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 comes backas:
[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 as preciouslydescribed, the return packet is:[0] 0x93 --> the user sent 0x13, which is not valid, so 0x93 returned[1] 0xA0[2] 0x02[3] 0x05[4] 0xAA[5] 0x55
The preceding examples 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 is:[0] 0x21[1] 0xA0[2] 0x02[3] 0x05[4] 0xAA[5] 0x55
assuming that the preceding values starting at Register 5 were actually written to the device.
SLAU286 – June 2009 USB-MODEVM Protocol 47Submit Documentation Feedback