Internal memory expansion

[gflorez]

Yes, a simple solution has to accomplish the rule of being simple....

[elmer]

Here are the PDF versions of the latest changes to the simple board.

It's mainly just a case of pushing some traces around in the hope of making it easier for the manufacturer to add tooling holes.

The other important change is to increase the size of the thermal reliefs on all of the ground pins in order to make them easier to solder (great tip from a friend!).

[dangerman]

I've been looking at this all day, and I'm afraid that I can't find any way to add that PDIP socket for the FLASH chip, and still end up with any kind of sensible board layout.

If you're going to program the chip in situ on the actual Enterprise, then you can still use the trick of swapping the order of address lines and data lines.

But maybe it's still too complicated to add the FLASH.

[elmer]

If you're going to program the chip in situ on the actual Enterprise, then you can still use the trick of swapping the order of address lines and data lines.

Yes, that's right.

But maybe it's still too complicated to add the FLASH.

It is, at least for me.

Putting everything on one side of the PCB makes the board so big that I think that I would have needed to add holes for the board-supports that the original EP128 RAM board uses.

It is safer to take things easy for my first board design.


I've responded to feedback from friends, and made another small change to the power rail on the board ... and it is finished (I hope)!

I've placed an SMT production order at JLCPCB, and should hopefully receive the populated boards in a few weeks.

If it works in my EP64, then I should have a few spare boards to sell on to anyone that wants one.

[dangerman]

Excellent work.

Btw, what program did you use to do the design?

[elmer]

Excellent work.

Thanks! Let's hope that it actually works!

Btw, what program did you use to do the design?

I used the free downloadable version of EasyEDA, initially because of its close links with JLCPCB, and LCSC (the Chinese parts distributor that owns both JLCPCB and EasyEDA).

Then I tried the free version of Eagle, thinking that it must be the more "professional" and "capable" solution, but I found it absolutely horrible to use, so I went back to EasyEDA.

[emptiness]

I've placed an SMT production order at JLCPCB, and should hopefully receive the populated boards in a few weeks.

Cool, what's the minimum order quantity?

If it works in my EP64, then I should have a few spare boards to sell on to anyone that wants one.

I'd definitely be interested

[elmer]

Cool, what's the minimum order quantity?

IIRC, the order quantity for PCB boards is in multiples of 5.

But they have a special option to order 5 boards but only get the SMT chips installed on 2 of the boards (for testing designs).

If you did that, then shipping and other overheads would significantly bump up your per-board price, but it would still be a good way to get boards made if nobody here has any to sell.

Once I've made sure that the design works, and have sold off the extra boards (I ordered 10 to keep the per-board price low), then I'll upload the complete set of design files and Gerbers so that anyone can order more boards in the future.

I'd definitely be interested

Thanks!

[emptiness]

One thing I've not yet understood is how the Enterprise senses the amount of RAM available. Does it probe memory on startup or is there logic in the RAM expansion to indicate how much RAM is present?

[geco]

i did not check, but i think it goes over the 02-FFh range and checks if it is RAM if yes, and the RAM is error free, it stores in the memory, if it finds  ROM, it checks if it starts with TEST_ROM or EXOS_ROM, if yes, then call it at address c00ah with different action codes, if i remember well 1st with ROM initialize, if it was successful segment of the ROM and start position of it's allocated memory if it has and on which segment, otherwise 0000h,00h is stored in system segment (FFh). So all available ROMs stored in FFh segment each have 4 bytes RAM definitions follow it, each RAM segment has 1 byte definition. Page0 segment is not in the list.

[dangerman]

One thing I've not yet understood is how the Enterprise senses the amount of RAM available. Does it probe memory on startup or is there logic in the RAM expansion to indicate how much RAM is present?

At startup, the EXOS ROM tries writing to each segment to check if there is RAM there. The hardware doesn't provide any extra information, it's tested by software.

[emptiness]

At startup, the EXOS ROM tries writing to each segment to check if there is RAM there. The hardware doesn't provide any extra information, it's tested by software.

Thanks geco & dangerman

[elmer]

The boards have arrived from China ... now I've got to wait for the headers to arrive, and then I've still got to wire up an RGB cable for my monitor before I can actually make sure that these work (or not)!

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[geco]

Looks cool

[dangerman]

Awesome news