HP 110 "garbage" on screen

[ThomasF]

(05-11-2023 08:11 PM)dave-in-kc Wrote:  Just to be clear, the example I posted earlier was of me typing each key twice. as in:
11223344...
qqwweerr...

Yes, I think it is very clear that it is every second character that is garbeled (char = char & 0xBF - ie bit 6 is clear).
Applying the same transformation on the top 2 lines, we can see that it says (so again confirming your findings):

Code:

MEMOMAKER
Line: 4 Column:21 Length

What is strange is that the background of the top 2 lines should be solid black (inverted), but starting with character at position 3 (if first is position 0, ie pos 3,11,19,27,...), the character is not inverted, and this then repeats with every 8 characters.
But, there is probably some ESC-sequence written to invert the display so we don't know exactly what and when it is actually sent to the display.
This might also explain why the "A" in MEMOMAKER is strange. It is shown as 0xB0 ("upperline"), but should have been 0x01 (SOH) since the actual character is 0x41.

I still think that the 16-bit to 8-bit latches are the most obvious cause to the problem, but it is easy for me to say
Would need an logic analyzer or oscilloscope and look at data coming in and out from the latches since the pins and soldering looks ok.

Cheers,
Thomas