Multimeter ICs
Revision as of 22:23, 1 November 2012 by Uwe Hermann (talk | contribs) (Fortune Semiconductor FS9922-DMM4)
This page lists some information about ICs commonly used in various multimeters (DMMs).
Fortune Semiconductor FS9721_LP3/FS9721B
FS9721_LP3 on Voltcraft VC-820.
FS9721 (?) on TekPower TP4000ZC.
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 | User bit 3 | User bit 2 | User bit 1 | User bit 0 |
Segment lettering:
| C | ||
| B | G | |
| F | ||
| A | E | |
| D |
Fortune Semiconductor FS9922-DMM3
TODO.
Fortune Semiconductor FS9922-DMM4
FS9922-DMM4 in a UNI-T UT61D.
The Fortune Semiconductor FS9922-DMM4 (datasheet) is a widely used 6000-count auto-ranging DMM chip: it takes input from the various controls on the front panel, drives the LCD display, and can communicate its readings via a serial port.
Protocol
TODO