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MDA/CGA/EGA to VGA Converter Released!

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Reply 200 of 341, by keropi

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retrocanada76 wrote:

try the new one, I turned the voltages back to 2.5V

I just tried the "I forgot to turn off noise filter for EGA" revision and it fixes those flashing pixels errors 😎

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Reply 201 of 341, by keropi

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I've been also meaning to ask about Jepael's pulldown resistors on the EGA port , is adding them an extra layer of protection for the EGA card? If one adds them then a new FW is needed to compensate for them?
Even with the existing boards adding pulldown resistors on the DB9 port is easy if one uses some 0603 or 0805 smd resistors soldered at the back side of the pcb.

Also is there a bootloader for the CoreEP4CE6 so anyone can update via USB and avoid clone programmers alltogether? The truth is most people like me will use ebay clones for programming that might be from good to utter bs quality 🤣
Is it even possible or this requires extra hardware?

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Reply 203 of 341, by keropi

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Allright thanks for the info!
Any recommendation of the value the pulldowns must be? Do they need to go to pins 2-3-4-5-6-7 or only needed for the secondary/intensity pins 2-6-7 ?

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Reply 204 of 341, by retrocanada76

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I think you can start with 4.7K or 10K, you need to feed all 8 pins of the 74ls245. If it was my board design this could be easily doable soldering one of these in the back of the 74LS245, connecting the ground to the common pin:

https://www.digikey.ca/product-detail/en/bour … 72LF-ND/3787777

Reply 205 of 341, by Jepael

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keropi wrote:

Allright thanks for the info!
Any recommendation of the value the pulldowns must be? Do they need to go to pins 2-3-4-5-6-7 or only needed for the secondary/intensity pins 2-6-7 ?

The rule is not to leave any input of CMOS chip unconnected. This means also situation where the cable is disconnected so all pins float.
So you'd need a pull-down on all eight lines, R,r,G,g,B,b,H,V.

Extremely good question on the pull-up values. I don't know what is optimal. If this was VGA, the HS and VS would be terminated with about 2.2 kohm to ground on today's implementations.
Keeping in mind that TTL high output is very weak, but this is usually driven with a 74LS244 bus driver, it can source about 3mA and sink 12mA. So the strongest pull-down tolerated is about 1kohm.
Since the converter board has very high impedance input, even a 100k would do. Maybe safe between 4k7 and 10k, so relatively high termination impedance.

That said, TTL input monitors might terminate with quite low impedance to get higher frequencies through the cable (it minimizes the R in RC filter, C being stray capacitances of wire etc).
For example IBM CGA monitor uses split termination with 330 ohms to 5V and 470 ohms to ground. That's 194 ohms termination into 2.9 volts.
The low termination value would help with signal reflections (it should match the characteristic impedance of the cable) and also help driving the TTL input buffer chip in the monitor, the IBM CGA monitor has 74S05 that requires the driver to sink 2mA for the input chip and about 10mA for the termination to make signal low, which is a lot. But the driver does not need to source much current at all to make signal logic high.
The monitor would see a disconnected cable as logic high level. It does not matter as because if there is no activity on syncs it keeps blank.

But in this case, as the unused pins need to stay low, it should be a pull-down resistor. If the FPGA is put into CGA or MDA/Hercules modes and ignores unused bits, then these can be pull-ups which suit better to LS TTL chips driving it. Maybe 4k7 pull-up?

I'd try on my converter board but currently I don't have any EGA/MDA sources. I'd try building a signal generator with a LS244 chip and wire to try pullup values and measure with a scope, but I'm afraid I don't have the resources to do that for some time.

Edit: Haha you got the same values but pushed submit first 😀 Yes, those are good values to try.

Reply 206 of 341, by keropi

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Thanks both for the replies 😀
It's not possible to use a hole-thru resistor network with the dreamblaster version because the LVC245 is a SMD device. So the only solution would be to solder 0603 single resistors either on the pins of the DB9 connector at the back or directly to the respective input pins of the LVC245.
I have 10K 1% 0603 resistors , I think I'll try with these.

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Reply 207 of 341, by Plasma

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keropi wrote:
I've been also meaning to ask about Jepael's pulldown resistors on the EGA port , is adding them an extra layer of protection fo […]
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I've been also meaning to ask about Jepael's pulldown resistors on the EGA port , is adding them an extra layer of protection for the EGA card? If one adds them then a new FW is needed to compensate for them?
Even with the existing boards adding pulldown resistors on the DB9 port is easy if one uses some 0603 or 0805 smd resistors soldered at the back side of the pcb.

Also is there a bootloader for the CoreEP4CE6 so anyone can update via USB and avoid clone programmers alltogether? The truth is most people like me will use ebay clones for programming that might be from good to utter bs quality 🤣
Is it even possible or this requires extra hardware?

I tested 4 different clone USB blasters and they all worked fine except for the super cheap ones (small black rectangular).

This is the cheapest one that I have found to be fully functional.

Reply 208 of 341, by ibmapc

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retrocanada76 wrote:

I think you can start with 4.7K or 10K, you need to feed all 8 pins of the 74ls245. If it was my board design this could be easily doable soldering one of these in the back of the 74LS245, connecting the ground to the common pin:

https://www.digikey.ca/product-detail/en/bour … 72LF-ND/3787777

I drew a red box on your board here to indicate the pins to connect the resistor network to. Does this look correct to you? Note the common pin connects to pin 10 GND.

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Reply 209 of 341, by retrocanada76

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Yup that's the idea. a bussed 8 resistor 4.7k will make the job. Job solder ir under the board.

it would be wiser to add a 0.01uf capacitor on this TTL as well.

I will make a version 2.01 later

Reply 210 of 341, by keropi

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retrocanada76 what do you mean by "it would be wiser to add a 0.01uf capacitor on this TTL as well" ? I don't understand where should this be added?

I also soldered my pulldowns as well - had to manually make the networks with 1% 0603 resistors but I think it turned out fine 🤣

x10InlUl.jpg

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Reply 214 of 341, by dreamblaster

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retrocanada76 wrote:

someone must donate one board full loaded to The 8-bit Guy for him to test 😀 he is doing a Tandy 1000 game....

I will send him one. I'm doing a small batch of 10pcs soon.

Do you receive my pcb, yet ?

Visit http://www.serdashop.com for retro sound cards, video converters, ...
DreamBlaster X2, S2, S2P, HDD Clicker, ... many projects !
New X2GS SE & X16GS sound card : https://www.serdashop.com/X2GS-SE ,
Thanks for your support !

Reply 215 of 341, by keropi

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retrocanada76 wrote:

add a ceramic 0.01uf capacitor between the VCC and GND but that's is optional.

hehe thanks
dreamblaster boards already have decoupling capacitors on board 😊

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Reply 216 of 341, by retrocanada76

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dreamblaster wrote:
retrocanada76 wrote:

someone must donate one board full loaded to The 8-bit Guy for him to test 😀 he is doing a Tandy 1000 game....

I will send him one. I'm doing a small batch of 10pcs soon.

Do you receive my pcb, yet ?

not yet 😒 but don't worry. I'm not in short of mce2vga 😀

If you send him a board, tell him about my project website and source code 😉

Reply 217 of 341, by retrocanada76

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New FW pals: stronger scanlines looks better 😀 and also I moved the OSD outside the border, just in case you want to get rid of them, so you can still see the OSD menu

enjoy

Reply 218 of 341, by dreamblaster

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retrocanada76 wrote:

If you send him a board, tell him about my project website and source code 😉

Of course I will, it is your project man, and it is a great project !
If there's any other information you'd like me to include in the letter (or maybe your photo ?) included in the box, just pm me.
It deserves youtube promotion, hopefully convincing people to boot up their old monitorless cga/ega/hercules/... pc's and have a fantastic retro experience on a vga screen.
I'm just here helping to make it available, and admiring.

Visit http://www.serdashop.com for retro sound cards, video converters, ...
DreamBlaster X2, S2, S2P, HDD Clicker, ... many projects !
New X2GS SE & X16GS sound card : https://www.serdashop.com/X2GS-SE ,
Thanks for your support !

Reply 219 of 341, by keropi

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I tried the new firmware , the scanlines are really stronger in this one! Maybe it's my 24" monitor but they are too strong for my taste tbh... is there a chance of a test fw that has scanlines at some middle value between this last fw and the ones we had until now?

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