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-   -   Ortonview PCB (https://www.vintage-radio.net/forum/showthread.php?t=181460)

SiriusHardware 29th Jul 2021 2:18 pm

Re: Ortonview PCB
 
Thanks, the posted version is quite readable actually. I see why you suggest track cutting prior to fitting the sockets.

Slothie 30th Jul 2021 2:49 pm

Re: Ortonview PCB
 
1 Attachment(s)
Well I tried loading the "clive" and "inside" graphics to the memory expansion and found I had huge "jailbars" down the screen. After my heart sank a little, and a little investigation I noticed that pin 40 of the PIC was bent and not in the socket... some fiddling around and I had the pins straight and all in the socket and they all went away. I played with the contrast some and the smearing is a lot better too.

When displaying from the memory I did notice a very slight occasional flicker on the normally blank digits of the display between the address and data fields, so there is still some bus interaction, but I'm not noticing any memory corruption yet. I've been trying to get my head around Karens code again, and so far it looks like there is at least a 3.75uS delay between asserting NENIN and driving the address pins, for example the smallest:
Code:

L5        BCF        PORTC,NSYNC                ; VDU on
        BSF        PORTA,NENIN                ; Nenin high here
        DELAY        D'13'
        BSF        STATUS,RP0
        CLRF        TRISA                        ; on hi 4 bus ~15(3.75uS after NENIN)
        CLRF        TRISD                        ; on lo 8 bus ~16 (4uS after NENIN)
        BCF        STATUS,RP0
        BSF        PORTC,NSYNC

This also explains why my buffers didn't work so well, as I was effectively driving the bus immediately on putting NENIN high! However, correctly implementing the buffers will mean that we can remove the constant switching of PORTA and PORTD between input and output which will give more timing headroom if we need other tweaks to the code, and possibly eliminate other loading effects,

I am trying to think of a way of arranging the firmware code so that its structure is easier to understand, perhaps using more macros for the more repetitive parts of the code. of course this will have to be done with regard to timing, but if I am successful the generated hex file should be identical....

NB: While loading the graphic images I was getting some corruptions because of the keypress timing, so I doubled the default values in send14. This rather crude tweak solved the problems, slowing the process but to be honest not enough to worry me. Id rather it be slow and reliable that quick and flaky. The alternative of course would be to switch off the VDU so it isn't slowing the MK14.

SiriusHardware 30th Jul 2021 3:07 pm

Re: Ortonview PCB
 
Yes, put simply, the system slowdown induced by the the VDU means that keys have to be pressed for a slightly longer minimum amount of time in order for keypresses to be reliably read, hence the need to slow down the uploader if the VDU is actively running.

That smearing is still, to be honest, much worse than it should be but I think you still don't have a short video-rated photo lead so we'll see what it looks like when the replacement arrives.

Slothie 30th Jul 2021 3:20 pm

Re: Ortonview PCB
 
Quote:

Originally Posted by SiriusHardware (Post 1394077)
That smearing is still, to be honest, much worse than it should be but I think you still don't have a short video-rated photo lead so we'll see what it looks like when the replacement arrives.

Yes, it is still bad but I have a better cable on the way, and I'm going to replace the output transistor as it got very hot while I was trying to solder it in and it might be underperforming..

SiriusHardware 30th Jul 2021 4:08 pm

Re: Ortonview PCB
 
"Photo lead?" (Phono lead, but you knew what I meant).

I've just arrived home to find the boards waiting for me, thanks for that. I'll put two pairs in the post to their respective future owners tomorrow (Saturday) morning.

Just today, I discovered that our little traditional electronics component shop down by the coast near here no longer opens on Saturdays, which is a big problem for me because my weekday working hours are the same as their weekday opening hours. I was relying on being able to go there tomorrow to get whatever misc parts I don't have, so that's a bit irritating. It means I'll have to scrape the parts together at work on Monday. I'll fit whatever I can find in the meantime.

Slothie 30th Jul 2021 4:39 pm

Re: Ortonview PCB
 
Quote:

Originally Posted by SiriusHardware (Post 1394106)
"Photo lead?" (Phono lead, but you knew what I meant).

I've just arrived home to find the boards waiting for me, thanks for that. I'll put two pairs in the post to their respective future owners tomorrow (Saturday) morning.

Just today, I discovered that our little traditional electronics component shop down by the coast near here no longer opens on Saturdays, which is a big problem for me because my weekday working hours are the same as their weekday opening hours. I was relying on being able to go there tomorrow to get whatever misc parts I don't have, so that's a bit irritating. It means I'll have to scrape the parts together at work on Monday. I'll fit whatever I can find in the meantime.

Glad they arrived safely! I tried packaging them so they wouldn't burst out the bag (I've had PCBs cut through padded bags before due to their sharp milled edges!).

I'm going to do a build guide for the uploader board because things are a bit fiddly re: clearances, but the main thing to remember is to either wire over the reset jumpers or fit a right-angle header, vertical headers will short on the Pi Zero with regrettable results!
If you're fitting flying leads for the reset they can be plugged onto the header too.
Its worth fitting the 2x20 header for the Pi in conjunction with the 16 way DIP socket as they fit flush together, and slight mis-alignment of one might stop the other fitting well as some of the holes are generous. The rest of the Opto Isolators have sockets provided by 2x18 way DIP sockets, or you could used strips of turned pin sockets for all the Opto Isolators. Or you could just solder them in, as they are unlikely to need replacing.

Shame your local shop stopped opening Saturdays. I'm surprised, if they rely on the hobby trade at all thats the best day to be open. I suppose they must mainly sell to businesses. Its a shame small operations are all passing away due to the internet, mind you there are a lot of new small operations that are internet-only so I guess it balances out, but there's no immediate gratification!

SiriusHardware 30th Jul 2021 5:07 pm

Re: Ortonview PCB
 
I've continued the discussion about the uploader PCB in the specific thread for that. For the OrtonView, I'm unlikely to have mine fully built before the early part of next week unfortunately.

Slothie 30th Jul 2021 6:06 pm

Re: Ortonview PCB
 
FWIW I've just tried the battery backup option and it doesn't seem to work. I might have a wiring error, but putting in the battery makes the PIC fail to reset, or switch between graphics and text mode alternately after reset, so something wierd is happening! I guess you can save yourself the cost of a coin cell holder....(unless I work out where the problem is).

SiriusHardware 30th Jul 2021 6:28 pm

Re: Ortonview PCB
 
Although it's a nice feature to have, and I have dug out a Hitachi 6116LP specially for the occasion, it's not a priority for me. So, in your own time. ;)

In the days when the only way to get code into the machine was to first type it in and thereafter load it from a tape, it would have been a brilliant asset (which is no doubt why Buzby took the trouble to battery-back some of his memory on 'Micky').

We use through-hole CR2032 type coin cell holders in a couple of products at work, but I don't know yet whether one of those will just drop in.

Slothie 31st Jul 2021 1:55 pm

Re: Ortonview PCB
 
2 Attachment(s)
Quote:

Originally Posted by SiriusHardware (Post 1394147)
We use through-hole CR2032 type coin cell holders in a couple of products at work, but I don't know yet whether one of those will just drop in.

I shouldn't worry yet, it crashes the PIC if you put in the coin cell. I think the problem is the "S" (select) pin on the RAM gets pulled down if the RAM is powered but the gate feeding it is not. I've a mod in mind using a MOSFET but I'm still working on that.

The great news is that I have fixed the video issue I am having, the not so good news is its because I made a mistake on the PCB - I used the wrong footprint for the transistor. However, you just have to solder it in backwards (with the flat side on the opposite side from the screen print) and it works great! It even works with my 5m long cable (the old cheapo one works sort of too but has huge interference because its not screened!)

So thats one thing to sort out with the V2 PCB... Apparently BC547Bs don't like having their collector and emitter swapped.

SiriusHardware 31st Jul 2021 2:08 pm

Re: Ortonview PCB
 
Thanks for the info - incredible that it was working as 'well' as it was under the circumstances. Will try to get the majority of mine built up on Monday. Tim's and Mark's boards are on the way to them so Tim should have his early next week, Mark's may take a little bit longer to get there...

Now that it's working that output from OrtonView is much cleaner and crisper than anything which comes out of my original SOC VDU - it was the same with the output from my OrtonView lash-up - now partly dismantled for parts for the 'proper' build.

Timbucus 31st Jul 2021 4:21 pm

Re: Ortonview PCB
 
Looking great - nice timing for the 81st Birthday of Sir Clive as well to post that Picture... looking forward to building mine and maybe finally putting together that origin of OrtonView video I have been planning - now I have a capture card people may be able to see Minefield actually running...

SiriusHardware 31st Jul 2021 5:21 pm

Re: Ortonview PCB
 
Although the 'Clive' image is fortuitously on-message we could do with a few more different 64 * 64 1-bit monochrome (not greyscale) images for display or 'slideshow' purposes.

Anyone know a photo editor which can (attempt to) produce such stringently limited images from bits cropped out of colour or grey scale photos? I drew Clive by hand but it was very time consuming building him up dot by dot - a lazier / easier way would be nice.

Tim, when you get a bit of time would you be kind enough to draw a sketch of your Plus-three (optocouplers) interface so I know which extra GPIO pins you used for which of the extra three, and which three connections on the MK14 edge connector the extra opto go to? I would guess you left the original thirteen routed as found and just added the others in to the gaps, but maybe not.

Slothie 31st Jul 2021 6:46 pm

Re: Ortonview PCB
 
1 Attachment(s)
Well I managed to use Gimp to produce this picture of me, the question is how to convert it to a bitmap suitable for the MK14....

SiriusHardware 31st Jul 2021 6:57 pm

Re: Ortonview PCB
 
Can you save it / attach it as a .BMP instead? (Is BMP even an allowed attachment format?). I wrote a clumsy bit of python to extract a 1 bit 64 * 64 pixel .BMP to SBASM3 .DB statements but it only works on uncompressed .BMP files. Good image, considering the mega low pixel resolution / colour depth.

Slothie 31st Jul 2021 7:08 pm

Re: Ortonview PCB
 
1 Attachment(s)
Quote:

Originally Posted by SiriusHardware (Post 1394416)
Can you save it / attach it as a .BMP instead? (Is BMP even an allowed attachment format?). I wrote a clumsy bit of python to extract a 1 bit 64 * 64 pixel .BMP to SBASM3 .DB statements but it only works on uncompressed .BMP files. Good image, considering the mega low pixel resolution / colour depth.

Hmm try this. Its in a zip because the forum doesn't like BMP files....

SiriusHardware 31st Jul 2021 7:15 pm

Re: Ortonview PCB
 
2 Attachment(s)
Along other lines, and regarding the problem with the battery backed memory... This (attached as both image and .zip in case the forum downsizes it too much) is the relevant section of the circuit for my early '1990s Maplin Z80 CPU card' which had three battery backed 6116 RAMs, the three ICs on the right in this image. This did work, so maybe you can look at a variation on this method.

In this particular case the battery is a rechargeable NiMH (which almost destroyed the board while I thought it was safely stored) hence R8, which is the trickle charge resistor for the battery. You won't need that in your version.

Note the address decoder is a 74LS139 with active low CE outputs.

The three left hand switches turn the battery backup for their respective ICs on and off. The right hand switch has nothing to do with the battery backup, it enables the NMI from the offboard display / keypad circuit.

Where they have used an OA47 (Germanium!) diode as a low-drop diode we would presumably now use a Schottky.

Slothie 31st Jul 2021 7:42 pm

Re: Ortonview PCB
 
Quote:

Originally Posted by SiriusHardware (Post 1394424)
Along other lines, and regarding the problem with the battery backed memory... This (attached as both image and .zip in case the forum downsizes it too much) is the relevant section of the circuit for my early '1990s Maplin Z80 CPU card' which had three battery backed 6116 RAMs, the three ICs on the right in this image. This did work, so maybe you can look at a variation on this method.

In this particular case the battery is a rechargeable NiMH (which almost destroyed the board while I thought it was safely stored) hence R8, which is the trickle charge resistor for the battery. You won't need that in your version.

Note the address decoder is a 74LS139 with active low CE outputs.

The three left hand switches turn the battery backup for their respective ICs on and off. The right hand switch has nothing to do with the battery backup, it enables the NMI from the offboard display / keypad circuit.

Where they have used an OA47 (Germanium!) diode as a low-drop diode we would presumably now use a Schottky.

Yes, it looks like they are decoupling the chip enables (pin 18) from the backup power using a common-base type transistor switch. My plan was similar, to use a MOSFET to create an open-drain inverter to replace U1C that inverts the chip select signal. I think that with the power off, the pullup on chip select is back-feeding power into U1 and possibly onto the main Vcc rail, causing latch-up or improper reset of the PIC. I wanted to take some measurements first. Once again the vital trace that needs cutting is on the top and runs near the DIP sockets!!

SiriusHardware 31st Jul 2021 7:55 pm

Re: Ortonview PCB
 
1 Attachment(s)
In the meantime you can amuse yourself by replacing the 'Clive' .DB image statements with the ones in the attached zipped .asm file. Note this is not embedded in a program to display the image, it's just the image converted to .DB statements so you need to cut and paste it into an existing 'displayer' program. It's obviously 512 consecutive bytes so best loaded into the 'new' RAM at 0200- and rendered by OrtonView from there.

I haven't tried this one, but I used the same wonky python program to extract the 'clive' image from the original .BMP to .DB statements.

SiriusHardware 31st Jul 2021 7:58 pm

Re: Ortonview PCB
 
Quote:

Once again the vital trace that needs cutting is on the top and runs near the DIP sockets!!
Can you cut the cross spars on the relevant socket out leaving only the two sides of the sockets left in the board? That will give you some leeway to see where you need to be.


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