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Amstrad Mega PC

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Reply 80 of 113, by Zalog

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keropi wrote on 2020-09-09, 12:50:

quite a bit cheaper I must add, no DHL shipping and no DHL import fees on top

Yes just found a local supplier - no shipping or import fees is a big bonus and does save a significant amount - I think I now know what I want for Christmas................ 😉

Reply 81 of 113, by keropi

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Jo22 wrote on 2020-09-09, 13:09:
I've got one of these flash carts (no name), too. Just recently, I was able to run some SMS games on it when inserting the casse […]
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I've got one of these flash carts (no name), too.
Just recently, I was able to run some SMS games on it when inserting the cassette in a Model 1..
This makes me wonder - does the Mega PC still allow the Z80 CPU to be the primary processor?
I don't mean to start an off-topic discussion, I'm simply curious. 😅
- Because some later Mega Drive units from TecToy didn't allow this anymore. Or so I heard. Phantasy Star 1 for Genesis was essentially the Master System game (with a built-in adapter) also.

here is the answer 😁

YO0nbvRl.png

@Zalog
the everdrive is also on my list, I have the very first mega-everdrive and it's been great from the start

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 82 of 113, by Jo22

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Thank you! 😎

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 83 of 113, by phipscube

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I've decided to try to get my Mega PC shipped from UK to me in Denmark, its highly unlikely I will be travelling back in October to pick it up.

I have 16MB of RAM ready to put in it and i've got some VRAM on the way. I also just bought a Ben Q BL702A monitor!

@Zalog, I noticed you have an Amstrad badge on your monitor... I had the same thought for mine so wondered where you found it? I've been looking on ebay etc for replica badges but haven't had much luck.. I'm considering spray painting the screen to match the Mega PC colour too.. I noticed a thread on here with details on how to do this: Best off the shelf spray paint for beige computer cases

@keropi, I've been thinking about how to make a clip on CPU that can be used to upgrade the standard Mega PC board with one of the many Ti 486sxlc2 50 CPUs floating around at the moment... and maybe even figure out how to put some L2 cache on it. Also, having a fly lead that could clip on or sit between an upgraded BIOS for the gate A20 patch.. I see you said you are waiting for some 486slc CPUs and wonder if you are having similar ideas? 😀

I was also thinking about your special card for Mega PC, and have a little request 😀 .. Is it possible to add a scanline mode for the megadrive output?

Reply 84 of 113, by Jo22

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Hi! I've seen these TI CPUs on several websites, too..
However, better be careful:

"G chips are 3.3 with 5v I/O.
0 designation chips are 5v.

So:
G50 = 3.3v
050 = 5v

Do not make the same mistake as me.
Requires a 50MHz bus to run at full speed.
"

Source: http://www.cpu-world.com/CPUs/80386/Texas%20I … LC2-G50-PQ.html

That being said,

Good luck! 😀

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 85 of 113, by phipscube

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Jo22 wrote on 2020-09-18, 07:47:
Hi! I've seen these TI CPUs on several websites, too.. However, better be careful: […]
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Hi! I've seen these TI CPUs on several websites, too..
However, better be careful:

"G chips are 3.3 with 5v I/O.
0 designation chips are 5v.

So:
G50 = 3.3v
050 = 5v

Do not make the same mistake as me.
Requires a 50MHz bus to run at full speed.
"

Source: http://www.cpu-world.com/CPUs/80386/Texas%20I … LC2-G50-PQ.html

That being said,

Good luck! 😀

Yes the G50 that can be found everywhere are only 5V I/O compatible... but I thought how some of the later clip on 486slc upgrades used 3.3V (5V I/O) CPUs with a regulator onboard.. this could be added to a new designed clip on board too..

I thought they ran on 25MHz bus and internally doubled to 50MHz?

There was an SXLC2 G66 made also that would require the 25MHz osc to be replaced with a 33MHz one, not a massive problem, but up to now i've not found any for sale anywhere..

Reply 86 of 113, by smsdave

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@keropi
I've been watching the Orpheus posts on the main thread with interest. I'm a bit of a newbie to soundcards from this era, I'm no audiophile but I would like to get sound effects for DOS games from my Mega PC. Two questions:
1) I've noted a few comments around about a MegaPC-specific card you have in mind, is that a different product you're planning in the next 6-12 months or so or does it just refer to the Orpheus as it stands?
2) While I can see there’s a lot of excitement around the Orpheus from those in the know, especially those wanting the PCMIDI features, are there features/benefits I’m likely to miss for my basic needs in the base model Orpheus compared to a second hand AWE64 soundblaster off ebay for £30-50 (e.g. https://www.ebay.co.uk/itm/Creative-Labs-Soun … rd/154088658502 )? I don’t want to deprive someone who would appreciate it more if it’s overkill for me.

On other topics…

Those of you looking at Krikzz everdrives, I’ve got several (for different systems); at this point in the year it’s worth holding on for Black Friday as he usually discounts a worthwhile amount then.

I’ve got some 8bitdo megadrive wireless controllers (https://www.8bitdo.com/retro-receiver-genesis-mega-drive/) for other devices but the dongles are too wide to fit into the hole around the recessed controller ports on the MegaPC. Does anyone have any bright ideas of adapters or similar I could use to extend the ports out somehow?

One thing, I managed to accidentally over order on VRAM so I’ve 6 chips going spare at cost if anyone’s in need in future.

@phipscube
I love the idea of spraying the benq monitor beige; will look forward to seeing photos of your results! I too am interested in a clip on CPU upgrade but haven’t seen anything for sale that looks like the easy upgrade I’m looking for.

Reply 87 of 113, by keropi

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@phipscube
well I got 2x 33mhz cpus but they are the 3.3v variants... should be 5v tolerant but I am not risking it
Zalog sent me a good 5v part the -25 MAB one which is the same Asmtrad used
at some point soon-ish when things calm down in my life I will attempt the upgrade and report back! (most likely when I'll get bored soldering the same thing over and over so I'll want a break 🤣 )
we'll see about a scanline mode - work has not yet started on this tbh

@smsdave
yeah the megapc-specific cards is an entirely different thing. It will not use the CS4237 chipset : it will use a 8bit SB chip that I will announce once things progress a little.
the megapc card will be a combo one: SB + CMS + OPL3 (see note below) + 10mbps NIC + covox dac + bootrom for xt-ide bios + 4mb dream-based synth + scandoubler for megadrive mode (will require 1 wire to be soldered to the megadrive card) and a header for an optional PCMIDI mpu with a single midi-out jack at the back (because there is no pcb space left)
So basically the goal is to make that single ISA slot to count and add things that will allow the system to be more easy and fun to use.

*about opl3 - there are 2 options that needs deciding and please anyone interested share your thoughts
1. do not use one and just have the amstrad's OPL2 + CMS chips essentially like having a SB2.0
2. do a very simple mod on the megadrive card (lift 1 pin and connect it with a solder blob to the next pin of a 74LS245) so OPL2 gets disabled and you are left with the OPL3 + CMS on the new card with a utility to switch modes: full opl3 mode or opl2 mode + cms

About the Orpheus card, well if you do not care about midi, wavetable header, opl3, s/pdif output then an AWE card (or whatever card for the matter) is perfectly fine... also these will continue to get made so it's not like there is a time window to decide and then they are gone - value your needs later 😀
I cannot make the claim of my card making all other soundcards worthless 🤣 it just has some features others don't and maybe someone likes them enough to buy one.
Truth be told one can perfectly game with a 8bit chinese clone card of the early 90s 😀

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 88 of 113, by Zalog

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@phipscube

The sticker is an old NOS one I found years ago for pennies - so not readily avaliable I'm afraid 🙁
The dimesions of it do scale out to the amstrad logo in this sticker https://www.ebay.co.uk/itm/Alter-Aufkleber-Do … 3oAAOSwO8pcA3Qe - but its a bit pricey and you'd have to cut out the logo from the sticker to be able use it, so not an ideal solution - but hopefully might give you a few ideas.

Really looking forward to seeing the Benq painted - it's something I had been considering, and will definitely be interesting to see what colour matches best 😀 - Good luck with the painting !

Reply 89 of 113, by smsdave

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Thanks keropi, appreciate the explanation, it sounds like I should wait for your all-in-one card at the moment.

My personal preference is to support reasonable operation without modding the original hardware so it's a trivially reversible upgrade just removing the ISA card but others may prefer the enhanced operation over that preference. That said the scandoubler does sound intriguing even if it requires a little soldering.

Reply 90 of 113, by Zalog

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keropi wrote on 2020-09-20, 19:39:

*about opl3 - there are 2 options that needs deciding and please anyone interested share your thoughts
1. do not use one and just have the amstrad's OPL2 + CMS chips essentially like having a SB2.0
2. do a very simple mod on the megadrive card (lift 1 pin and connect it with a solder blob to the next pin of a 74LS245) so OPL2 gets disabled and you are left with the OPL3 + CMS on the new card with a utility to switch modes: full opl3 mode or opl2 mode + cms

Hi Keropi, my thoughts would be retain the OPL2 chip for two reasons - firstly it would keep the sound more "period" - I have a fair bit of nostalga for OPL2 sound and the megapc does sound special to me 😉
The second reason is that it doesn't require any modification of the megadrive card and its components, which adding an OPL3 would - thus the MegaPC could be quickly returned to a stock machine just by removing the ISA card.

Dispite this position, I do fully support the addition of a scan doubler and its required wire - I do think it is vital for these machines survival and although we currently have Benq monitors as a suitable display replacement, that model isn't likely to be around forever - so as this trivial mod would still allow the machine to be returned to stock by pulling the new card (abet leaving a wire with a plug attached to the Megadrive board) it's well worth doing and gets my vote 😀 .

Reply 91 of 113, by Jo22

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Hi, sorry for intrusion. But from what I remember, a pure AdLib clone (OPL2) listenes to port 388h/389h only. Unlike SB1/SB2 clones, which also have OPL2 accessible via their ports in addition.
So this makes me wonder if the OPL3 simply can't be told/tricked to ignore these legacy addresses and use the Sound Blaster ports only.
If I'm not mistaken, a real SB Pro 2 or SB16 card has OPL3 -in addition to center/mono audio at AdLib's legacy ports- at SB base+offset.
So that's 220+something or 240+something, simplified. So if done correctly, in a perfect world, programs expecting a Sound Blaster will try the SB addresses first,
whereas a legacy game will find OPL2 at AdLib's 388h/389h. Anyway.. A lot of "ifs", I know. 😅

Edit: Some typos fixed.

Edit: These are just some thoughts of mine. I don't mean to discourage anyone. I know that such projects are.. challenging.
If there wasn't so much to wire up, I'd also encourage to make that OPL2 pin software-controlled (in theory, not really feasible here).
Say by using a simple address decoder, a DOS utility and a flip-flop. A relay or an optoinsulator+pull up/down resistor would then connect/disconnect the pin.
I know, that's very simplified and must look very naive to an advanced electrican.. 😊

Edit: Or just add a tiny on/off push-type switch at the back off the card that goes to the OPL2 chip and it's corresponding pin on PCB ?
I'm not sure if that's possible, due to the lenght of the wire (picks up noise ?).
Also, a reed relay switch perhaps could be used instead of a normal switch, to avoid the need for drilling a hole ?
- Just attach a little magnet at the back of the MD card to turn on/off the OPL2.

Edit@Zalog I could be wrong, but you don't have to necessarily disable that OPL2. At least on the hardware side, nothing should break because of this.
Except for the CMS logic thing, I see no issue. But since the CMS in on another card, the danger should be low.
Normally, if you have two same chips, OPL2 or OPL3, in the system, they should play in sync to each other.
That's because they are write-only devices (they only listen to their ports, write no data back)..
If you inter-mix OPL2 and OPL3, worst thing that should happen: The game in question goes silly during auto-detect phase.
Or, you will hear noise comming out of one of each chips (the OPL2, likely, since it doesn't support the OPL3 features such as 4-OP mode).
The excepion to this is the seldomly used YMF289. It can also be read back and uses 44,1KHz samplinng..
https://en.wikipedia.org/wiki/Yamaha_YMF262#Yamaha_YMF289

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 92 of 113, by keropi

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Well thanks for the inputs - really appreciated and it led to more thinking:

First of all CMS support needs to be removed completely.
It will never be fully gameblaster compatible anyways and it just stands in the way of a simpler design.
It is just a cool thing to try for some games but other than that it does not offer anything more. What do you guys think of this?

Second, there will be 2 modes for the onboard opl3:
a. it will just answer on the SB port queries leaving adlib port for the stock opl2 (so some program/game will be able to use the sb ports to communicate with opl)
b. it will take over if sega-card opl2 is disabled: opl3 will answer in both adlib and sb ports

so one can decide the level of modding he wants to do...
the single wire for the scandoubler cannot be avoided however - it is a requirement for the thing to work

oh and scanlines are possible to implement 😀

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 93 of 113, by phipscube

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@smsdave I have tried to find a clip on solution too but had no luck... so started to think how I could make my own with one of those Ti 486SXLC G50 CPUs. I can't seem to find the 100 pin QFP clip on sockets now either so maybe its going to take some time to figure out what to do, if anything at all.. haha! 😀

@Zalog, thanks for the link! I saved it just incase, but yes its a bit pricey for a sticker... I have since thought how i'd like the matching wine red 90s Amstrad logo thats on the Mega PC... I found the logo online and found some clear printable labels... so maybe I can make my own. As for paint for the monitor, I found a place in Poland that actually sells Amiga 500 and C64c beige in a can! https://retrohax.net/shop/amiga/spray-paint-amiga-500-beige/

I'm not sure if thats quite the same but regardless, he's currently not able to ship outside Poland..

I found alot of the older PCs match up with Ivory Bisque.. but I think the Mega PC has a bit more white to it... the 90s PC were like that. I'll wait until I have my Mega PC back to check more accurately 😀

@Keropi

My vote goes with opl3 support and the small mod, i'm probably going to mod my MD card with Tiidos sound improvements anyway.... but if most people prefer no to mod then i'm good with the opl2 + CMS. At least as long as I can get voices in games then I don't mind the Mega PCs poopy ad-lib sound... haha! Its kinda charming with them old warbly jingly jangles 😀

As for the CPU, yeah i've seen the 25MHz MAB 486slc too and have considered getting one and being safe with 5V... the clip on mods tend to be unreliable anyway, but the 'to the maxx' itch gets under my skin so can't help thinking about a 50 or even 66MHz Mega PC.. haha... My sensible side is saying leave the poor old 386sx as is if it doesn't gain much performance anyway and just run what works with that, 512KB VGA GFX and 16MB RAM from the period.

Scanlines! Yeah! 😁

Last edited by phipscube on 2020-09-30, 11:56. Edited 1 time in total.

Reply 94 of 113, by keropi

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@phipscube
thanks for the feedback!

but to be clear CMS supports is as good as gone... so in the card there will be an OPL3 and the user will chose either to mod the sega card and use OPL3 full time or do not mod the sega card and opl2 will work along with opl3 (in this case opl3 will only "answer" to SB ports not adlib one)

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 96 of 113, by Zalog

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keropi wrote on 2020-09-24, 11:15:

but to be clear CMS supports is as good as gone... so in the card there will be an OPL3 and the user will chose either to mod the sega card and use OPL3 full time or do not mod the sega card and opl2 will work along with opl3 (in this case opl3 will only "answer" to SB ports not adlib one)

That sounds fab - that gives everyone the best of both worlds - I've had problems with two devices on the adlib line (Civilisation was one culprit), so not modding the sega card and having the OPL3 only responding on the SB ports is an excellent solution !

@phipscube
Keep us posted how you get on with the sticker printing - there's definitely a gap in the market there at the moment !

Reply 97 of 113, by keropi

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currently performing the 486slc upgrade but after removing the 386sx cpu that patch wire makes little sense:

uMAxpTnl.jpg

yZK5k4kl.png

those cache pins are all non connected on the mobo... will still attempt it but I don't have high hopes

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system

Reply 98 of 113, by jmarsh

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I thought we figured that out? It connects Pin 22 (data output bit 1 / A20 gate control) on the 8042 keyboard controller to A20M# on the CPU. The CPU needs to know what state the A20 gate has so it can know if bit 20 of an address should be ignored or respected when looking up data in its internal cache.

Reply 99 of 113, by keropi

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jmarsh wrote on 2020-09-26, 12:13:

I thought we figured that out? It connects Pin 22 (data output bit 1 / A20 gate control) on the 8042 keyboard controller to A20M# on the CPU. The CPU needs to know what state the A20 gate has so it can know if bit 20 of an address should be ignored or respected when looking up data in its internal cache.

so what you are saying is that even though it's pin30 #KEN on the cpu that is removed the actual connection is on pin31 A20M# ?
all that so they have 2 pads to solder?

ZkILDR3.jpeg

🎵Link to buy a PCMIDI mpu
🎧Orpheus soundcard project
💻WTB Amstrad PC7486SLC-33 system