Victor protocol
Many digital multimeters made by Victor share the same protocol. At least the Victor 70C and Victor 86C support this protocol. In the 70C this is generated by a chip inside the device, on the 86C it's in the cable.
USB interface chip
Reverse engineered pinout of the unknown USB/HID chip:
| RXD | 1- | O | -20 | |
| 2- | -19 | |||
| 3- | -18 | |||
| 4- | -17 | 5V | ||
| 5- | -16 | |||
| 6- | -15 | |||
| GND | 7- | -14 | D+/- | |
| 8- | -13 | D+/- | ||
| 9- | -12 | |||
| 10- | -11 | ~6MHz clock (?) |
Protocol
The device registers on the USB host as a HID-class device ("Boot Interface" subclass), see lsusb.
The protocol payload is 14 bytes of data which can be read from endpoint 1, at no more than 1 Hz. The 14-byte chunk is somewhat obfuscated. To deobfuscate, subtract the ASCII value of the following string from each of the 14 bytes in turn: jodenxunickxia. Then reshuffle the bytes into different positions, according to the following table:
| Original position | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 |
| Final position | 6 | 13 | 5 | 11 | 2 | 7 | 9 | 8 | 3 | 10 | 12 | 0 | 4 | 1 |
The deobfuscated payload is then structured as follows:
| Byte | Bit | Value |
|---|---|---|
| 0 | Unused (always contains 0x50). | |
| 1 | Unused (always contains 0xb0). | |
| 2 | Flags. | |
| 0 | Minus. | |
| 1-7 | Unused. | |
| 3 | Major measurement modes. | |
| 0 | Voltage measurement mode, combined with AC or DC flags in byte 6. In combination with the Diode flag in byte 4, signifies diode testing mode. | |
| 1 | Current measurement mode, combined with AC or DC flags in byte 6. | |
| 2 | Resistance measurement mode. In combination with the Continuity flag in byte 4, signifies continuity testing mode. | |
| 3 | Unused. | |
| 4 | Frequency measurement mode. | |
| 5 | Capacitance measurement mode. | |
| 6 | Temperature measurement mode, in degrees Celcius. | |
| 7 | Temperature measurement mode, in Fahrenheit. | |
| 4 | Value factors and extra measurement modes. | |
| 0 | µ (Micro). | |
| 1 | m (Milli). | |
| 2 | k (Kilo). | |
| 3 | M (Mega). | |
| 4 | Continuity (in combination with resistance mode in byte 3). | |
| 5 | Diode (in combination with voltage mode in byte 3). | |
| 6 | Duty cycle measurement mode. | |
| 7 | Unused. | |
| 5 | Extra flags and value factors. | |
| 0 | Unused. | |
| 1 | Unused. | |
| 2 | Max measurement mode. | |
| 3 | Min measurement mode. | |
| 4 | Unused. | |
| 5 | Unused. | |
| 6 | n (Nano). | |
| 7 | Unused. | |
| 6 | Flags. | |
| 0 | Unused. | |
| 1 | Unused. | |
| 2 | Auto-ranging mode. | |
| 3 | DC measurement. | |
| 4 | AC measurement. | |
| 5 | Relative measurement. | |
| 6 | Hold mode. | |
| 7 | Unused. | |
| 7 | Decimal point position. | |
| 0 | No decimal point. | |
| 1 | Rightmost (1 digit after point). | |
| 2 | Middle (2 digits after point). | |
| 3 | Leftmost (3 digits after point). | |
| 4 | Unused. | |
| 5 | Unused. | |
| 6 | Unused. | |
| 7 | Unused. | |
| 8 | Unused (always contains 0x04). | |
| 9 | Least significant digit on display. | |
| 10 | Second digit from right. | |
| 11 | Second digit from left. | |
| 12 | Most significant digit. | |
| 13 | Unused (always contains 0xd4). |