Here's some information on the Fluke's display, in case it's helpful to anyone...
* The LCD is controlled directly by the Fluke's processor, with the display data being latched with CMOS LCD drivers.
* The data bus consists of lines W, X, Y, Z; which is 2
3, 2
2, 2
1, 2
0 respectively.
* HV and DP lines are also part of the data.
* The BP signal is a 50Hz signal only used for refreshing the stock display. Not needed for a custom display.
* Display data is latched with positive pulses on one of the five strobe lines (ST0 - ST4).
* Data is valid on both rising and falling edges of the strobe pulse. (I grab the data on the rising edge.)
* Strobe 0 (ST0) latches data for U10, which handles the HV, BT, and REL indicators.
* A high on DP during ST0 indicates REL.
* The battery (BT) signal comes from a voltage dividier and PNP. I don't use this, since my Fluke doesn't have those components.
* ST0 also latches data for U11, which handles the plus(+), minus(-), 1 (first digit), and the dB indicator. W line is for minus(-), X is for plus(+), Y is for dB, and Z is for the "1". Note that the plus(+) is actually two segments, so W *and* Y together turn on the plus.
* ST1 latches data for U12, which is the second digit (first whole 7-seg digit).
* ST2 latches data for U13, which is the third digit.
* ST3 latches data for U14, which is the fourth digit.
* ST4 latches data for U15, which is the fifth digit.
* U16 handles the decimals, and is latches by each of the strobes (ST1 - ST4).
* The display-only data can be taken from the display board ribbon, or rather the vias right next to it.
* Functions (Volts, Amps, Ohms...) are only available at the Fluke processor (which is why I made a carrier board).
* Ranges (2, 200, etc.) are also only available at the Fluke processor.
* The Vss pins of the chips runs at -5V.
* The Vdd pins of the chips runs at 0V.
* Display data is latched in sequence: ST0, ST1, etc.
* A strobe pulse is about 168us wide, though I observed some at 116us. This isn't really useful anyway.
* There is about 216us between the falling edge of one strobe to the rising edge of the next.
* One cycle is pretty short, so it makes sense to grab all the data and then process it after ST4 is done.
* The whole cycle repeats about every 410ms.
Range switch logic (pins are of Fluke 40-pin processor):
| Pin 3 | Pin 4 | Pin 5 |
Range | RngA | RngB | RngC |
200 ohm | H | H | L |
2k ohm | L | H | H |
20k ohm | H | L | H |
200k ohm | L | L | H |
2000k ohm | H | H | H |
2M ohm | L | L | L |
200 nS | H | L | L |
2 mS | L | H | L |