First, I've already started work modifying the PCB layout of the prototype for 32-pin DIP flash chips, which will mean more flash (the 28-pin chips are very hard to find, anyway).
Yes, by all means, 32 pin DIP for flash. I've got scads of TSSOP-32 chips, but I can make DIP carrier boards for those.
...I doubt there'd be much disadvantage to loading it to RAM instead of to flash. The way the EASy68K program works is similar to having a SBC with *just* RAM, and it would be a similar program, load code, run paradigm.
My only reason for having a non-token amount of flash would be to allow the possibility of standalone operation, or having multiple boot images installed (e.g. be able to boot into EhBasic, or some monitor program, or...) Also, flash is cheap enough, and smallish flash chips are hard to find (as you mentioned already).
I'd like to use newer components, and I actually have a handful of 68SEC000 chips on my desk as I type (I think the 68HC000 is now hard to get, but the 68SEC000 is still available through common sources). From my working 68008 prototype, though, it'd be a do over. I don't have a lot of free time at the moment, so this wouldn't be something I could do quickly.
As for my 'inventory'; I've got about 10x DIP48 68008-8, about 30x 68901 in PLCC, a few DIP48 68901, and about 10x DIP40 68681. I'd love to use these (saved from scrap a long time ago).
The 68008 in DIP48 is a bit frustrating because it's limited to 1MB address space, and /IPL0 and /IPL2 inputs are sharing a pin (so IPL is limited to 0, 2, 5, or 7). Another shortcoming of the 68008 (vs. 68EC000, for example) is that /VMA is not bonded out.
The difficult 68901 function to replace would be the vectored interrupt capability.
Fully agree! Yep, I'm right there with you - it makes an awful lot sense to keep a 68901 in the circuit, if only for the purpose of being able to to bask in the glory of vectored interrupts. All the more desirable with a DIP48 68008 where there's only three interrupt levels to play with. I took another look at the 68901 UM and realize that the UART isn't so crappy after all; seems as if it will support 19.2kbps with a 3.686MHz xtal.
The components themselves aren't prohibitively expensive, but the PCB space taken by LEDs, switches, buttons, and all the rest could mean tens of dollars of cost. PCBs manufactured in small quantities are pricey, and they are priced based on board area.
Again, I fully agree. I've already gotten the "front panel" and das Blinkenlights nostalgia bugs out of my system. Spending $50-ish on mechanical hardware that won't really get used is not so interesting to me, at this point.
A general comment: to me, the primary benefits of an SBC that is "EASy68K compatible" are:
1) a (wonderful) windows-based IDE and simulator.
2) a well defined and standardized BIOS (i.e. TRAPs for IO, etc)
Perhaps a good starting point is to determine the MINIMUM system hardware and BIOS configuration, and then we can freely build above/beyond the minimum to our heart's desire.
For example, the 68008 system you described seems a good candidate, but maybe tweak things a bit:
10 MHz MC68008 CPU (mine are all 8 MHz...sob..weep..)
128K RAM --> maybe bump up a bit?
32K flash --> maybe bump up to 128K (i.e. 1Mbit Flash)
- UART terminal connection
- vectored INT controller
Beyond that, I think it's A-OK if you and I and others end up with drastically different hardware. I think this is almost a given:
1) we all have different "parts on the shelf" at our disposal - it's painful and expensive to track down these old devices in very specific packages. (my experience from the N8VEM CP/M project)
2) different philosophy on "glue" logic implementation - I'll almost certainly use a MAX7000 CPLD (I have 'em, I know 'em, I like 'em) for address decode, missing VMA logic, DTACK/BERR/VPA generation, clock tree, etc. Others may want to use GALs, or 74xx, for their own designs.
That being said, when I get around to making a 68008 system, I'll certainly make the Schematic and PCB fab files available and offer to sell at cost any excess PCB (I tend to use OSHPARK, and so the minimum lot size is 3 pcs) to anyone that wants them.
Thanks again. Let's keep the conversation going.
I agree! tomcircuit at the domain that sounds a bit like "bee whale"