My Dragon cartridge boards (actually work!!!)

[Rink]

Actually... looking at it now, I think iTead might have undercharged me (sent out a lot more boards than quoted) for the PCBs. They're like a few mil over the maximum width so maybe they took pity on me.

As I said, great company.

[zephyr]

They came in at a truly horrendous £4.30 each (excluding any shipping costs + tax). The problem is the size of them - they're slightly too big for the price bracketing used by the PCB fab (see below). If they weren't made to fit wobble-free in a standard Dragon Data case then they'd be like half that cost.

The PCB price is a little high, but not too bad. I would be willing to pay about $15 - 20 each (including postage) for a slightly modified version of this PCB with just a 28 pin IC socket fitted (for inserting a 27128/27C128 - 16K EPROM).

And now a small request: Please upload a picture of the underside (solder side). I'm pretty sure that most people would want to see the solder side of that very interesting looking board.

Sure thing. Will do as soon as I get home (I didn't think to take one) - no passing judgement on my soldering abilities mind.

I look forward to viewing that later!

[Rink]

The PCB price is a little high, but not too bad. I would be willing to pay about $15 - 20 each (including postage) for a slightly modified version of this PCB with just a 28 pin IC socket fitted (for inserting a 27128/27C128 - 16K EPROM).

Never played with a 27 - have you ever tried reading from a 27 series with Vpp (pin 1) at ground instead of the recommended Vcc?

[zephyr]

No!

[Rink]

Drat - can't get an anywhere near usable photo tonight, there's just not enough light.

I should stump up for some decent light bulbs.

[prime]

So how are you reading the EEPROM as a matter of interest ?

The super lazy way...

From memory (Cartridge -> ROM):
!CTS (pin 32) is connected to the ROM's chip enable.
R/!W (pin 18) is connected via the jumper to Write Enable.
R/!W (pin 18) is connected through a NAND gate (wired to invert) to Output Enable*

Addresses A0-A14 are connected to the relevant input on the ROM. Note: this means that ROM/RAM's which don't have A14/A13 (e.g. 8K ones) must have those pins not connected internally. Some SRAM chips use A13 as a second chip enable which (I tried it accidently) means that half the RAM would be disabled for bits of the cartridge address range.

The address wiring is bad of course - the available 16K cartridge address range on the Dragon would require a 32K ROM/RAM chip if A14 was connected. But there were reasons why I did it this way - mostly laziness.

That seems resonable for a parallel device, but in that case what's the little 8 pin device to the bottom of your board ?

Cheers.

Phill.

[Rink]

That seems resonable for a parallel device, but in that case what's the little 8 pin device to the bottom of your board ?

That's just a dual NAND gate IC for inverting R/W. Only using one gate of it but I have so many of the things that I just threw it on for convenience.

[zephyr]

Drat - can't get an anywhere near usable photo tonight, there's just not enough light.

I should stump up for some decent light bulbs.

I suggest you take it to work and snap it either indoors or outside in the daylight. I'm really interested in taking a good look at the solder side of that board.

Regards,
Steve

[Rink]

I suggest you take it to work and snap it either indoors or outside in the daylight. I'm really interested in taking a good look at the solder side of that board.

Finishing work earlier today so it should be light when I get home - will try this afternoon. Promise.

[zephyr]

Thanks!