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Hello everyone!

I'm trying to write some eproms with the Dragon 200E data, and as I cannot rewrite for whatever reason the original 27128 eproms that came with my Dragon 200, I decided to write a couple of 27256 chips, duplicating the content just in case.

Thing is, I managed to burn them properly (at least reading them back yields the same data that was written) but they don't work at all on any Dragon board I've tried.

The original 27128 chips are one 250ns and one 300ns access time, while the 27256 are 170ns access time, which should be no problem.

So, does anyone has an idea what could be happening?

Hi Rob! Hope you are well.

Are you writing the image to the upper 16K of the 27256? A14 should be high as this is the /pgm pin on the 27128.

One way to be sure is to write the same 16K image to both halves of the 27256.

Hi Stew!

Yes, I made sure to copy the contents twice.

It’s quite weird, as a couple of times I managed to get it working, but as soon as I turned the Dragon off and on again, it won’t start anymore...

That is strange. The only other thing I can think of is that Vpp (pin 1) should be connected to +5V for normal read operation. Behaviour is undefined or erratic if connected to 0V or left floating.

Well, you were on the right track there

I asked a friend of mine at the CPCWiki, and he pointed out, that A14 must be tied to +5 or Ground for it to select the high memory addresses or the low ones.

It turns out that connecting A14 to Ground makes them work and I now have successfully transformed my Dragon 200 into a 200E!

Oh, happy day!

I had to use two sockets sandwiched together, and solder a cable between A14 and ground.

Here are a couple of pictures for your viewing pleasure, and a big thank you for your kind help!