Multimeter ICs

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Protocol

The chip periodically sends 14-byte packets at 2400 baud, 8n1. The upper nibble of each byte indicates the byte number. The payload is composed of the lower nibbles, and is a 1-1 mapping of the LCD segments. The downside to this protocol structure is that transmission errors in the LSB nibbles cannot be detected. There is no checksum or CRC in the packet.

Packet structure

Byte Bits 7-4 Bit 3 Bit 2 Bit 1 Bit 0
0 0x1 AC DC Auto RS232
1 0x2 Negative 1A 1B 1C
2 0x3 1D 1E 1F 1G
3 0x4 DP1 2A 2B 2C
4 0x5 2D 2E 2F 2G
5 0x6 DP2 3A 3B 3C
6 0x7 3D 3E 3F 3G
7 0x8 DP3 4A 4B 4C
8 0x9 4D 4E 4F 4G
9 0xa u n k Diode
10 0xb m  % M Beep
11 0xc Farads Ohms Rel Hold
12 0xd A V Hz Low battery
13 0xe hFE Celsius Reserved Reserved

Segment lettering

  C  
   
B G
   
  F  
   
A E
   
  D