Plotting anecdote

[dthrone]

Sort of hardware related...

'Back in the day' in the 90s, like a lot of people I got my cartridges from Trade In Post in Shropshire.  One weekend my Dad decided to drive over there because they'd repaired our disc drive and I was going to pick a new cartridge.  The guy in the shop said they'd just got in a new batch of cartridges and he appeared with Plotting.

So I excitedly took it home, fired it up on our 6128+ and... the monitor went haywire.  A few days later the cartridge got sent back and they posted out another one.  The same thing happened with the  second one!  We gave up and I ended up swapping it for Batman (I think).

They sent a note with the Batman cart saying they'd got to the bottom of the problem with the Plotting carts and they only worked with black and white monitors.  What??

I'm not sure why I just thought about this.  Is there a hard or soft reason this could be true or does it sound like BS?

For anyone who didn't have the opportunity to visit the shop they had all the carts neatly stacked in a glass cabinet, it's probably the most plus carts you'd ever see in one place at one time!

[Gryzor]

Where's that from? I remember reading it before.

[dthrone]

Where is what from?


I can't remember if I'd mentioned this specific thing before, I know I posted about the specific features of some of my Trade In Post carts quite a number of years ago because they're known to be the ones taken out of the demo units so were unfinished in some ways (especially Pang).


Either way, I've definitely not figured out if how a cart could only work on a black and white monitor if it is true.


Edit:  Oh if you mean the anecdote, it is my own! 

[Gryzor]

Haha yeah I meant the anecdote, I'm pretty sure I've read it before so I thought you were quoting, didn't realise it was yours!

[dthrone]

Judging by the lack of offers of explanations for how the cart could only work on a B&W monitor I'm guessing the shop was probably mistaken.

It would be interesting to know if anyone else picked up a Trade In Post Plotting and had any problems though.  Maybe it was one dodgy cart and they just sent the same one back to me or possibly a dodgy batch which is how they acquired them.

As I sort of implied in the original post, they got these carts in later than the selection they were originally offering.  This is also clear in the AA ads.  They also had instruction books for the Plotting carts but no boxes (I still have the instruction book  ).  Most of their carts were sold loose with a plain label, I think the Plotting carts had proper labels although it was 25-30 years ago so don't quote me!!

[zeropolis79]

I've got a Switchblade cart with a type-written label - not a proper printed label - could that have come from the same source.

[Xyphoe]

I'm pretty sure that Plotting wasn't one of the games in the demo units ("Comparator") used in shops, so was likely a legit cartridge. I have the cart from the boxed version but it works fine on my Amstrad CM14 colour monitor.
So not sure what happened there!

[GUNHED]

Using the C4CPC today, does it now work with color monitor? Or is the effect still there?

[dthrone]

Using the C4CPC today, does it now work with color monitor? Or is the effect still there?

I'll get my colour monitor down from the loft at some point to try this out.




I just had a look at the cart file, the CRTC R0 is set to &40 not the usual &3F.  I don't understand monitors or the CRTC well enough to know if this could be the potential cause of a problem on particular monitors?




Still assuming there was something in what Trade In Post said 


Further to the above, info I read on the Grimware website below.


So it seems like this really could be the issue and the problem is real - unless anyone wants to correct me?  In which case Plotting is essentially bugged and won't work on all monitors.


I noticed on the wiki page for Plotting this CRTC setting is noted but the potential consequences are not explained.




REMEMBER: Be monitor friendly


No matter what you are doing with the CRTC, from setting up a simple fullscreen to any complex split-screen frame structure, to keep friendly with the monitor :


YOU MUST NOT program HSync time-discontinuities (R2).
YOU MUST NOT program VSync time-discontinuities (R7).
If you break any of these rules, your program will produce bad video-timings for a short time and will make the monitor display jump and/or distort for some time (depending on it's hardware settings).


YOU MUST program the CRTC to produce an HSync each 64us which last for at least 8us (R3).
YOU MUST program the CRTC to produce a VSync each 19968us.
If you break any of these rules, your program will produce bad video-timings. Some monitor may tolerate it, but some others WILL NOT! (I'm not kidding!).

[zeropolis79]

I've used Plotting on my C4 on my colour monitor 6128 Plus with no issues..

[dthrone]

Interesting. 

Where the Grimware site says "Some monitor may tolerate it, but some others WILL NOT! (I'm not kidding!)", I don't know what factors would affect this, like purely model or manufacturing tolerances within a model range or something.

I know for a fact it didn't work on my CM14 using two real Plotting carts, not C4CPC.

Need some input from a forum expert please

[Skunkfish]

So, the question is.... do you still have the same 6128 Plus and monitor to test again (some 25 + years later)

[dthrone]

So, the question is.... do you still have the same 6128 Plus and monitor to test again (some 25 + years later)

Yes, the exact monitor and 6128+ but no real Plotting cart, they both got sent back to the shop and swapped for Batman!! 

[Skunkfish]

Just tried on my 6128+ (can't believe I've never played Plotting before) and it was working fine (CM14 monitor).
I'm assuming the .CPR I'm using is a straight rip...

[dthrone]

I used the .cpr from CPC Power this morning (in Winape) just to check the CRTC values.  I'm not aware of any alternative versions floating around.


I can try out with my GX + C4CPC and the original monitor in the next day or so.

[dthrone]

CONFIRMED


Tonight I tried Plotting on my GX+C4CPC with the original CM14 monitor - the screen is messed up, see pic below.

I modified the Plotting cart image to set CRTC R0 to &3f and it now works with the same set-up! 

I've attached the modified .cpr file.  The offending byte is at &2b3 in block 0, I think this can only be a cock up by the programmers forgetting they were counting from zero not one.

This is definitely a 'show stopper' bug in that it would have resulted in returns (as I did twice myself).  I still don't know what portion of monitors this would affect - I'd love some input on this from someone.

So Plotting joins that exclusive club of GX games that had an official release but have a potentially crippling bug (No Exit being the other where the programmer forgot to place the stack pointer)

[GUNHED]

Used the Plotting CPR which came with the C4CPC and it worked flawless on the color monitor.


Can it be a problem of different CPRs, CTM versions or 6128Plus mainboard revisions. I let you know if I find out.

[dthrone]

Used the Plotting CPR which came with the C4CPC and it worked flawless on the color monitor.


Can it be a problem of different CPRs, CTM versions or 6128Plus mainboard revisions. I let you know if I find out.

That would be great 


So to be clear the situation -

   
• The .cpr sets CRTC R0 to &40 not &3f
• I had a real Plotting cartridge on my 6128+ with CM14 monitor -> fail
• I had a .cpr file running via C4CPC on my GX4000 with same monitor -> fail
• Modified .cpr file that sets CRTC R0 to &3f using same monitor -> works
• Therefore conclude the issue is with the tolerance of the monitor to CRTC R0 setting

In addition, I think Trade In Post's 'only works on black and white monitors' comment was a red herring.  I suspect they tried the cart on a colour monitor and it didn't work then tried it on another system with black and white monitor and found it did work.

[Skunkfish]

We just need to find a bunch of people with a CM14 monitor to see if any of them can reproduce the issue....
And get some 464Plus and GX4000 owners on board as well 

[dthrone]

We just need to find a bunch of people with a CM14 monitor to see if any of them can reproduce the issue....
And get some 464Plus and GX4000 owners on board as well 

Yep and still holding out for a monitor/CRTC boffin to explain about monitor tolerance to the R0 setting

[kawickboy]

In the late 90s I ordered carts from Trade in post. They recycled old Arnold-V test carts. Stickers were home-printed and their pang weren't well burned (no introduction), and my Robocop 2 had sprites glitches. At the beginning Plotting weren't in their catalog. With original carts I have no more issue.

[dthrone]

In the late 90s I ordered carts from Trade in post. They recycled old Arnold-V test carts. Stickers were home-printed and their pang weren't well burned (no introduction), and my Robocop 2 had sprites glitches. At the beginning Plotting weren't in their catalog. With original carts I have no more issue.

Rather than home burned I think they were supposed to be taken from (or at least intended for) the demo units that were destined for shops as Xyphoe mentions above.  This has been discussed in older topics but some carts weren't the full release, presumably rushed out for the demo units before the games were completed.  Pang being the notable example with no intro, background graphics missing, the aeroplane sprite missing, no level select, different background to Stage 1, quite a list actually...  In fact the way the blocks are arranged in the cart is even different to the full version.  Actually it would have been interesting to hear what Stuart Middleton had to say about this in his recent interview with Xyphoe on Youtube!

Still holding out for an explanation of factors affecting monitor tolerance to the programmed CRTC R0 value - I have been trying to figure it out, a bit complicated