Chinese scales usually have a four-pin output port on the side of the scale that sends the scale position data to the DRO. There are four different protocols used for sending this data:
- 24BIT - Two 24-bit, binary numbers are sent with the first representing the absolute position and the second representing the relative position. The two numbers are counts with a resolution of 20480 counts per inch.
- 21BIT - A single 21-bit, binary number is sent representing the absolute position. The number has a resolution of 2560 counts per inch. The 21BIT scales differ in that the DRO must provide a clock to read out the data rather than the scale providing the clock like other Chinese scale types. See the 21 bit protocol information at the ShumaTech web site for information on how to connect a 21 bit protocol scale.
- BIN6 - A single 20-bit, binary number followed by a 4-bit flag field. The 20-bit number is the count with a resolution of 2540 counts per inch when the scale is in metric mode.
- BCD7 - A single 24-bit, BCD number followed by a 4-bit flag field. The BCD number represents the seven digits shown on the scale display.
In addition, the 24BIT and BCD7 scales support a "fast" mode where they send the data to the DRO at a much higher rate than normal. The 21BIT and BIN6 scales do not support that feature.
The metal backs of Chinese scales are connected to one of the battery terminals. For 24BIT and BCD7 scales, the metal backs are connected to the positive battery terminal. For 21BIT and BIN6 scales, the scale beams are connected to the negative battery terminal. If you mix both types on one DRO, then you must insulate them to avoid shorting the DRO power supply through the machine.