TIL311s as the 7-segment displays?

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Matt Balmer

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Jul 23, 2022, 1:15:50 PM7/23/22
to PAL 6502 computer
I wonder what modifications to the schematic (and the ROMs) would be necessary to switch out the 7-segment displays for some TIL311s. I've seen a number of bus reader devices on Tindie showing up that use these really cool old hexadecimal displays, and since they're basically self-contained (logic and everything is inside the package) it makes me wonder what you would need to alter to make them work properly.

Obviously, all of the seven segment driver transistors and resistors wouldn't be necessary, but I'm betting that the ROM would need to be changed to output data to the displays in line with what it's expecting. 

Would there be anything else I'm missing? 

Here's a link to the datasheet for the displays: https://www.jameco.com/Jameco/Products/ProdDS/32951.pdf
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Hendrik-Jan Megens

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Jul 23, 2022, 1:51:35 PM7/23/22
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Not sure what happened, my message appears to have been deleted.

Anyway, trying again:

These TIL311' s can be hard to find, you may want to try the DIS1417 in stead (drop in replacement).

Note that they are quite powerhungry; I made a bus monitor for my RC2014, but it is drawing a bit much for the 7805 to drive both the RC2014 and the bus monitor, due to the power consumption of these displays (same apparently for the 311).

I'm going to try posting this without link, hope it works better, but for reference Google 'Scott Baker bus monitor'.

Cheers,
Hendrik-Jan

Matt Balmer

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Jul 23, 2022, 2:04:01 PM7/23/22
to PAL 6502 computer

Yeah, I'm aware of the DIS1417s, too -- and I remembered seeing that they can be power-hungry, but that's kind of why I'm asking the question -- if I wanted to modify the PAL-1 to take these instead of the seven-segment displays, what would be necessary? I'm not actually envisioning it as an external bus monitor, but as a literal replacement for the existing 7-segment displays on the PAL-1 board. I did see that Scott used another product to help offset the power drain issue -- a "drop-in" switching regulator. The original product he linked is no longer available, but there's now a 3 amp version instead that looks like it would be perfect.

Jim McClanahan

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Jul 23, 2022, 2:31:54 PM7/23/22
to Matt Balmer, PAL 6502 computer
The TIL311s take a 4 bit input (that would be between $0 and $F hex) and display the hex value.

The KIM/PAL has seven separate output lines that the ROM (and other software) turns on (or leaves off) as needed to display whatever is desired. There is a table in ROM that translates a hex value into the combination of seven segments needed to display the hex value.

The KIM/PAL also continuously refreshes the display as it polls the keypad for input. If you jump to some code that doesn't explicitly keep the display "on", it will blank. That is different than latched output like the TIL311 where you put the 4-bit value you want in, strobe the latch line, and the display holds the value until you either strobe or blank it.

Since they are fundamentally different, you would have to rewrite the ROM code. Getting the right character for the right value would probably be fairly easy--you just would map $0 to $0, $1 to $1, etc. and use 4 bits of the 7 that are available for output. (You could probably even skip the lookup table and free up a few bytes that way.) You would have to handle the strobe signal which could be done with one of the 3 unused lines I suspect. (And maybe use another one to allow blanking.)

You would not be able to run any of the original code that drives the individual segments.

From a "wiring it in" perspective, it probably isn't overly difficult. (You would need to figure out an adapter circuit for the TIL311 to the wires used for the seven segments.) The software probably wouldn't be overly difficult either since the ROM source code is published. (There are only a few dozen lines of assembly code associated with driving the display.) The end result would be "one of a kind" and not compatible with anything that uses the display beyond calls to the ROM routine. (So things like Hunt the Wumpus or most stuff from the Book of KIM isn't going to work.)

Thanks,
Jim W4JBM 

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Matt Balmer

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Jul 23, 2022, 7:41:00 PM7/23/22
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Hm. Well, then it sounds like doing something that would end up making it so that original software runs on it with those displays instead is not a trivial matter, since the way they operate is fundamentally different. Sounds like it would take something that intercepts the signals sent to the display lines and translates them to what the TIL311s expect, but that would be . . . kinda a bit much to tackle for not a lot of benefit -- especially if it ends up breaking a lot of original software, too.

John Kennedy

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Jul 25, 2022, 9:40:31 AM7/25/22
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Yeah, it would be more trouble that it's worth to replace the existing 7-segment displays with TILs. However, the TIL displays are still brilliant - and ideal for connecting to the RIOT expansion for experiments. You could patch* the ROM call that displays a digit to write to the TIL, and see what happens. I suspect you could use the TILs for entering data and examining memory at the very least. Worth trying and letting us know :-D


*Burn a new ROM

GN L

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Jul 25, 2022, 10:13:58 AM7/25/22
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The TIL displays has some vintage beautiful, but is too smart for KIM-1 ROM.

I think some expansion boards dedicated to TIL displays are more reasonable.
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Best,
Liu

John Kennedy

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Jul 25, 2022, 10:33:39 AM7/25/22
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Oops yes the routine I was thinking of (OUTCH  $1EA0) to display a character is really for the serial terminal output, not for the 7-segment displays. That said, the KIM/PAL stores the value displayed on the LEDs in memory locations $F8 to $FB, so you could patch code that wrote to those addresses to write somewhere else so any RIOT connected TILs could display those values. It would be a fun project. 

Hans Otten

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Jul 27, 2022, 3:06:10 AM7/27/22
to PAL 6502 computer
An expansion board with a 6522 VIA and 6 TIL311 is easy to construct (but quite expensive).
Write F9 FA FB is easy for such a display, patching the KIM-1 ROM  routine. 

Even more fun would be a TFT screen ...
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