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http://archive.worldofdragon.org/phpBB3/viewtopic.php?f=8&t=2989
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).Rink wrote: 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.
I look forward to viewing that later!Rink wrote: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.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.
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 wrote: 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).
That seems resonable for a parallel device, but in that case what's the little 8 pin device to the bottom of your board ?Rink wrote:The super lazy way...prime wrote:So how are you reading the EEPROM as a matter of interest ?
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'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.prime wrote:That seems resonable for a parallel device, but in that case what's the little 8 pin device to the bottom of your board ?
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.Rink wrote: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.
Finishing work earlier today so it should be light when I get home - will try this afternoon. Promise.zephyr wrote: 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.