daveejhitchins wrote:I have been able to recover the contents of the cartridge version of the BASIC editor PLD
daveejhitchins later wrote:I'll still do the .jed to fuse map exercise though (it's the Cartridge version of the .jed I have - But the schematic of the Single ROM version - Doh!).
I know there are differences between the two versions. However, at this stage, in order to understand how the whole system is suppose to work, would it be helpful to use the cartridge version of the .jed. (with any extra diodes) and then ignore the outputs for the extra ROM/RAM socket?daveejhitchins also wrote:I gave-up on the .jed to fuse mapping as soon as I looked at the data I have. I realised that the cartridge also has some decoding for the extra ROM/RAM socket. So I must have used a few more diodes in the address decoding. This would make it meaningless for the stand alone version.
Do you remember which came first, the cartridge version or the single DIL ROM version? I presume, as the Electron owner was your primary market, development work mainly took place on Electron systems.
The thought that occurred to me, was that during the original prototype phase (or what-ever you called it) back in the day, you found problems. Some forum members recently (last two or three years) have found unexpected glitches that can affect SRAM contents (when a SRAM is used as sideways ROM). So maybe during development work some similar problem was found. As a result, the PLD and the ROM were altered to “work-around” the discovered problem. Maybe a second flip-flop? Maybe that's what some of this unknown memory accessing is doing? Of course, I'm just guessing here
The pin 1 ROM to PLD connection problem. Are you sure that the ROM pin 1 is only connected to the PLD?
Often EPROM Vpp is connected to +5V. But not always (see below).
Can you think of any reason why the PLD would need to have an input to detect if it was in a ROM socket?
Beeb ROM sockets:
<Link>retroclinic wrote:Pin 27 is tied high, but in a Model B pin 1 is floating, and not connected to anything, therefore unless you tie it, using a 27512 will give unpredictable results.MartinB wrote:....No, you can use them as 27128's by just programming the relevant quarter. In the Beeb, pins 1 and 27 are tied high at the rom sockets and these equate to a14 and a15 on a 27512.
It's best to perform this mod:
To use 27512s (and SWR if you want it, or just leave the SWR bit out), that way you get the full benefit and can use one as 4 different ROM images.
I'm sorry if this just adds more confusion