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. Note: The USB/HID chip is in the multimeter (not in the USB cable/connector) for this device. The device is connected to the PC using a standard USB cable (without any internal logic/chip).

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).