One of the steps I described earlier was to map the LCD segments to the LCD driver chip pins and then to the internal memory of those chips.  This is because when I receive that data in my microprocessor I will have to be able to interpret it.

I first examined the LCD display itself and carefully followed each pin to a segment.  I ended up with this sketch:

Then I used a special set of HP probes on the DMM in continuity mode.  The probes are super tiny and have spring probe tips like used for PCB test probing.  I followed each LCD pin back to the driver chips.  That led to this:

1S and 2S represent the two LCD driver chips.  It turns out 2 is the low order and 1 is the high order addressed chip but that doesn’t matter.  The S number is the segment output number of the chips.  The 7 segment below has the standard segment labeling.  Still looks confusing?  Patience…  Now I put the segment outputs in order and get:

LCD Driver 0 segment outputs
S0      10 MHz A
S1      10 MHz B
S2      10 MHz C
S3      10 MHz D
S4      10 MHz E
S5      10 MHz F
S6      10 MHz G
S7      Decimal point
S8      1 MHz A
S9      1 MHz B
S10      1 MHz C
S11     1 MHz D
S12      1 MHz E
S13      1 MHz F
S14      1 MHz G
S15      PROG
S16      100 kHz A
S17      100 kHz B
S18      100 kHz C
S19      100 kHz D
S20      100 kHz E
S21      100 kHz F
S22      100 kHz G
S23      RX
S24      10 kHz A
S25      10 kHz B
S26      10 kHz C
S27      10 kHz D
S28      10 kHz E
S29      10 kHz F
S30      10 kHz G
S31      EXTERNAL
S32      1 kHz A
S33      1 kHz B
S34      1 kHz C
S35      1 kHz D
S36      1 kHz E
S37      1 kHz F
S38      1 kHz G
S39      CH

LCD Driver 1 segment outputs
S0     100 Hz A
S1      100 Hz B
S2      100 Hz C
S3      100 Hz D
S4      100 Hz E
S5      100 Hz F
S6      100 Hz G
S7      MHz
S8      10 Channel A
S9      10 Channel B
S10     10 Channel C
S11     10 Channel D
S12     10 Channel E
S13     10 Channel F
S14     10 Channel G
S15     Right arrow
S16     1 Channel A
S17     1 Channel B
S18     1 Channel C
S19     1 Channel D
S20     1 Channel E
S21     1 Channel F
S22     1 Channel G
S23     Left arrow
S24     HI
S25     M
S26     LO
S27     F
S28     K
S29
S30
S31
S32     Bar graph L
S33     Bar graph M
S34     Bar graph H
S35
S36
S37
S38
S39

Now it makes sense, doesn’t it?  So now I can decode the binary data sent to the LCD drivers.

I looked at the LCD driver chip data sheet (PCF8576) and see that there are both command and data words.  Most of the command words have to do with LCD configuration and I can ignore them; I will have to pay attention to the cursor index set command but that is trivial.

To be continued…