C1P video mod -- double characters per line.

[drwass2]

I have a "simple" mode to the super board II that gives twice as many characters per line.
I designed this mod 35 years ago, so I'm going from memory here but this is the info.
It requires a few cut traces (I believe it is about 4).
It requires 2 simple 7400 series TTL chips.
Almost all of the required signals can be picked up via empty plated through holes that are easily available. I soldered pins into these holes and use wire wrap for the mod. The chips are placed in the empty dual inline area avaible on the board.
How it works.
One of the TTL chips is used as a monostable vibrator to generate a new "DOT CLOCK". a Trim pot is used to adjust this.
This begins at the start of each character and generates the horizontal dot clock for the character. It is faster then the original .
The rest of the circuit, the other TTL chip, selects the RAM line based on the odd/even character address, thereby interspacing the characters
from two lines into one video display line. The result is that you get twice as many characters accross, the two characters fitting exactly into the horizontal space of the original OSI but without the "dotty" look. Actually looks real nice.
Since we still the RAM from the line below, the next video line underneath is blank, so there is reasonable spacing between the lines vertically.
Now for the software. Since each alternate character comes from a RAM location 32 characters ahead we need to replace the normal display routine with software that knows this and compensates. I wrote this in a few bytes that can fit in the unused low bytes available.
If people are interested I will dig out my machines and try to publish this fantastic mod.
It is very easy to change back and forth from the old OSI to the new with a simple 1 bit control. This means that by mapping this bit to a
unseen video bit (one extra TTL chip) we can even control it via software. It can even be controlled on a line by line basis via software.
SWEET.
I should have published this 35 years ago. Please leave some posts here if interested.
DrWass2

[MK14HAK]

Dig them out please...

[BillO]

Yes, interested...

For sure this needs to be recorded for posterity.

[dave]

Definitely try to find them. This would be of great interest to many C1P owners.

Dave

[drwass2]

I wasn't sure many were even reading stuff her, so now that I see a lot of interest I will try to find my OSI.
I know its all in a box somewhere and pretty sure it all works. tough part will be finding a monocrhrome monitor that works.
May have to hack into a CGA monitor. Anyway, I'll see if I can find the schematics of my mod and start to at least explain it to you guys.
Need a couple of weeks because busy now and WIFE will slow me down for sure. You guys probably know about that.
DrWass2

[drwass2]

Well i found my box of OSI stuff after 30 years in storage and hooked it up.
I used a modern flat screen LCD monitor which had old analog video in (yellow, white, red RCA connectors).
it worked quite nicely giving very clean sharp (square dots) output. looks better on old tube where dots blend a little.
A little problem with sticky keys. but seems to clear up if you just hit them a lot. some miss and some double up.

My video mod still works perfectly. While trying to figure out how to load the software to control the mod and the screen output I found some old Cassette tape recorders and proceeded to read the 30 year old tapes. Amazing to me!
Forgot how to load the tapes and what format I saved them in...so have to relearn the OSI stuff again.
Anyway while running a little game program I wrote in BASIC which scans the keyboard and moves things on the screen the machine got flaky. resetting was not consistant and if I got to the D/ W/ C/ M/ screen it would sometimes not respond to the C key. finally it just doesn't work at all. Tried pulling all chips in sockets and resetting them. No change.

Spent the last few hours trying to debug this and seems to have been traced back to the keyboard read and write enable signals (RKB and WKB )not coming out of U20. futher tracking seems to show that the barV signal gointo into pin 4 U20 is not getting there from pin9 of U23. Need to do a little more debug on this before trying to replace U23 (not in socket) Have to check my stash of chips to see if any in stock.........yes I have a few. looks like some desoldering work tomorrow if WIFE doesn't get in the way. (you know how that is).
If I can get it running I'll show some photos of my Video mod. How do you insert photos here????
drwass2

[dave]

If I can get it running I'll show some photos of my Video mod. How do you insert photos here????
drwass2

That's great news. To insert photos, find the "Upload attachment" tab just below the post entry box. Click it, and select your photo to upload. Once you've uploaded all your photos, each one will be listed below the post, along with a couple of buttons, including "place inline". If you click that, it will add the photo into your post at the cursor.

Dave

[drwass2]

thanks for the info on adding photos. I will have some in the future...
My machine which was running perfectly, suddenly went south. I thought I traced it to the 74ls138 chip which decodes the address for the video and keyboard. I verified this by taking out the CPU and playing with address lines 13,14,15. chip would not decode so i removed it and managed to mangle up the printed circuit a lot (iron too hot) but I patched it all back together, put in a socket and new chip but still would not work. Things at the chip seemed ok but I noticed that address line 8 was stuck high. All others and all data lines were moving around. So i thought a bad chip may be sucking on the address line. I removed all the memory chips and roms, put in just the Monitor Rom and one set if RAM chips at 0. Still no working so changed the cpu and it actually came up ok. cleared the screen and put up the D/ C/ W/ M/ prompt.
hitting enter and enter again got a memory size of 255 bytes or something like that. figured I was home free, put back all the chips and then not working again. the macine powers up with garbage in video memory, usually hitting reset will clear the screen and put up the prompt.
Now is does nothing..... Not sure whats up....replaced cpu again, this time with a 65SC02. does anyone know if any problems with using this chip. (I understand it has extra instructions and certain fixes). Sometimes it works, clears the screen, puts out the prompt but won't resond to any keys. sometimes it jumps into what looks like monitor mode with 4 numbers and then 2 numbers usually 0000 00. I still think its got something to do with addressing to get to the keyboard. Will get back again....Wife thinks I'm spending too much time with that "old crap".

[drwass2]

So, at this point, I have just the monitor ROM and 1 line of RAM plugged in. No BASIC roms
System seems to consistently come up with video garbage on power up (this was always normal).
Reset clears the screen and put out the prompt, but no response to any keys.
If I keep hitting the reset it doesn't seem to always do the same thing. sometimes a "D" will appear in random spots on the screen.
sometimes it will give 4 and 2 numbers at top left as if in monitor mode.
At this point, I have a dual trace oscilloscope and a logic probe that shows hi, lo, open, pulse. This is what I used most.
looking for pulsing on the address and data lines.
I will next break out a gadget I won ( Elektor Magazine contest). which can monitor 8 lines. will try to see what addresses it is going to.
Have to learn how to run that pico scope so another learning curve.

Is there a disassembly of the ROMS available somewhere? I wrote my own disasembler in basic 35 years ago and found some of my print outs of a lot of the stuff, missing a call to setup the ACIA which is somewhere in beginning ROM. At first I had a baudot teletype(30 baud) which I wrote an ASCII to Bardot driver and bit banging code to put data out one of the lines of the keyboard port which drove the teletype machine through a transistor. Worked very nice. Had to do some strange substitutions for nonexistant characters. I think I had a weather printer.
I later acquired a teletype model 28 (printer only) which had the moving key platten that had upper and lower case, red/black ribbon and even 1/2 line feed forward and back so you could even print things like H2O correctly. Even had a Centronic model 101 brand new, still on pallet which I never used. Sold it on ebay many years later. Also sold the model 28, donated the baudot tty to MARCH here in NJ.
MARCH is a vintage computer club here...MidAtlanticRetroComputerHobbiest....They have a rather complete museum of vintage computer stuff at Camp Evans Area part of InfoAge. You can google it.
well got to work now.... will look at C1P later tonight...any help or suggestions ???

[drwass2]

Worked on the board again tonight and got it working.
Looks like I had a bad RAM chip also.
My main goal was to get the video to clear (shows the processor is running some code) and give the DCWM prompt and then respond to the "M" input showing it can read the keyboard. I took out all the BASIC ROM chips and all but one set of RAM.
When it worked, I added RAM one set at a time until error occurred. That is the bad chip!!! Put the BASIC ROMs back and still working..

Not sure if I can load my video processing code without all of ram. will look into that later.
thanks guys.