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Upgrading the original ROMs in a 32KB Microbee - Printable Version

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Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 03-01-2021

Hi,

I'm sorting out my Microbee's and want to sell one of them.

It's got these ROMs installed at the moment, including BASIC 5.10.

As they're HN462532s, if I want to replace them then I'll probably have to wipe and reprogram them as 2732 pinout is slightly different (although I could hack something I guess)?

If my programmer will bother with something so small.

Maybe I can use some 2764s with an small adaptor to match the 462532 pinout.

Is the IC34 available for an additional ROM if I solder in a socket?

Thanks

Brett

Oh, and can I install BASIC v5.29?


RE: Upgrading the original ROMs in a 32KB Microbee - ChickenMan - 03-01-2021

I wouldnt upgrade the Basic, as later Basic assumed other options were fitted and would stop working. 5.22e might be okay. What speed does the bee run at, the early 2khz or 3.375khz (what is the crystal speed next to BASIC rom B) ? If 2, then the PLAY command would be wrong with a later Basic also.

Those early coreboards were set for 2532 eproms as that was around at the time, later boards had options for 2732 to be used changing some jumpers and 2764's physically wont fit. That spare IC34 can take a 2532 and was for the NETwork. Code there starts at E000h. The EDASM roms could be changed to one of the games roms thats in the repository with 1/2 the 8kb rom code in each of the 4k roms. I can burn 2532 roms if that helps.


RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 03-01-2021

Awesome, thanks for the advice. My cheapo Chinese programmer doesn't know anything about those 2532s - I do have a US-made programmer that could, if I get a US$59 adaptor for them. So nothing I can do myself this afternoon - I couldn't even read them to see what they contain (well, it's pretty obvious now).

I was thinking of hacking together a little adaptor board for the 2764s - they would overhang and I'd be wasting half the ROM, but I have plenty and I can program them ... but is probably not worth the effort.

It sounds like I'd be better off selling as-is ROM-wise.

So basically there's BASIC 5.10 in A/B/C/D and then EDASM in the last two.

Brett.

Oh ... speed - I can see a crystal marked 12.000 ... ?

Oh x 2 ... thanks for the offer for burning new 2532s!


RE: Upgrading the original ROMs in a 32KB Microbee - someone - 03-01-2021

It seems that your BASIC comes from the short era when the last MWBASIC ROM was serialised.
A while after that, batches of masked ROMs were created with the serial number dropped (in an attempt to lower production costs).
However to have masked ROMs made incurred a NRE tooling cost thus a substantial quantity was required to negate these costs.
Masked ROMs are easily identified by their lack of sticker and UV window and also by the special production markings upon them.
The masked ROMS weren't just limited to the MWBASIC ROMs.  They were also used for the Dual Font ROMs (on 13.5MHz) machines.

It's pretty simple to kludge up or obtain a replacement coreboard if that is your desire. Many others have done it.
It's even simpler if you drop the battery backup requirement.
The left connector contains all of the address A[0..15]  and data D[0..7] lines along with the feedback /ROMSEL signal.
The right connector contains the power pins +10 and GND, the system control signals and a few decoded I/O port address select outputs.

Although not applicable to your case, the simplest coreboard consisted of two small boards; one with just a single ROM and PLD; and the other with a voltage regulator and connections to come control signals. These boards plugged into their respective sides of the baseboard and attached together with a small ribbon cable. It was designed specifically to provide access to the whole baseboard to simplify and expedite repairs. The little board didn't any RAM because the baseboard's CHAR and PCG RAM could be used after it had been proven to work by the ROM's diagnostic routine.

In your case, you could use later generation 32K SRAM, 16K ROM, 8K ROM and 4K ROM for the simplest standard coreboard set up for a 2MHz machine.


RE: Upgrading the original ROMs in a 32KB Microbee - ChickenMan - 03-01-2021

If your Eprom burner can handle 2732, you just need to make up an adapter to allow it to burn 2532's, which is what did, and its all explained here - https://atariage.com/forums/topic/269633-replacing-a-tms2532-with-a-2732/ or here http://www.thegleek.com/bobroberts/mspacrom.html


RE: Upgrading the original ROMs in a 32KB Microbee - Ernest - 04-01-2021

Hi Brett,
The first question I would be asking myself is "What do I want to achieve with upgrading?"
You need to set a a target before you spend too much time on how to get there.
The second question is "will this improve the attractiveness to a potential buyer or detract from it?"
Lastly "Will the cost outweigh the improved resale value?"
Assuming the keyboard is working well my top items for improving resale value would be.
A) Upgrade to 13.5Mhz (from the current 12MHz which will require a new Character ROM on the mainboard (which will be needed if you go to a later BASIC anyway), as well as a new crystal and some board mods..
B) Adding deglitch to get rid of those black streaks from the screen.
C) After the above, then look at other possible Coreboard changes that would be attractive (Do I aim for a gamer or programmer as a buyer?)

Hope this helps

Ernest


RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 05-01-2021

(04-01-2021, 12:20 AM)Ernest Wrote: Hi Brett,
The first question I would be asking myself is "What do I want to achieve with upgrading?"
You need to set a a target before you spend too much time on how to get there.
The second question is "will this improve the attractiveness to a potential buyer or detract from it?"
Lastly "Will the cost outweigh the improved resale value?"
Assuming the keyboard is working well my top items for improving resale value would be.
A) Upgrade to 13.5Mhz (from the current 12MHz which will require a new Character ROM on the mainboard (which will be needed if you go to a later BASIC anyway), as well as a new crystal and some board mods..
B) Adding deglitch to get rid of those black streaks from the screen.
C) After the above, then look at other possible Coreboard changes that would be attractive (Do I aim for a gamer or programmer as a buyer?)

Hope this helps

Ernest

Thanks for your reply Ernest, some good points.

When I re-sell a computer, and especially when people are paying premium prices, I always want it to be in the best condition possible ... none of this "no cables, can't test, dunno" and the images show it caked in grime because they haven't bothered to even give it a wipe down (argh).

I want the new owner to be able to actually use it - power it, connect it to a screen, load software (if nothing in ROM) ... the plan ... hope ... is to at least break even Wink

We had an Amstrad growing up, and Apples/XTs at school, so never had much hands on with Microbees, although they always fascinated me.

So it's good to hear about those improvements I could do.

Like someone mentioned about new core boards, had anyone made (i.e. PCB files available) a modern/simplified replacement that can take 32KB SRAM and 2764/27128 ROMs?

Brett.


RE: Upgrading the original ROMs in a 32KB Microbee - Ernest - 07-01-2021

Quote:Like someone mentioned about new core boards, had anyone made (i.e. PCB files available) a modern/simplified replacement that can take 32KB SRAM and 2764/27128 ROMs?

Brett.

I have been working on a new SRAM / ROM based coreboard design (MB8328 functionality) for a while now, using some of the more readily available higher density components. I.E. 62256 (32K in one chip), but still sticking with the through hole format. 
As there would be little demand for such a board, it has been on the low priority list. 
I have not yet sent it off for a first production run and therefore validate my layout, so at this point is not yet tested.
I expect on a small run to equate to about $20 - $25 per bare board.

Ernest


RE: Upgrading the original ROMs in a 32KB Microbee - g67wjjk - 07-01-2021

(07-01-2021, 12:41 AM)Ernest Wrote:
Quote:Like someone mentioned about new core boards, had anyone made (i.e. PCB files available) a modern/simplified replacement that can take 32KB SRAM and 2764/27128 ROMs?

Brett.

I have been working on a new SRAM / ROM based coreboard design (MB8328 functionality) for a while now, using some of the more readily available higher density components. I.E. 62256 (32K in one chip), but still sticking with the through hole format. 
As there would be little demand for such a board, it has been on the low priority list. 
I have not yet sent it off for a first production run and therefore validate my layout, so at this point is not yet tested.
I expect on a small run to equate to about $20 - $25 per bare board.

Ernest

That sounds exactly what I'd like to have.  I guess you could also allow for larger capacity EPROMs, using DIP switches to select which banks are actually active - save you having to physically replace EPROMs if you wanted to switch between ROMs.

Brett.


RE: Upgrading the original ROMs in a 32KB Microbee - ChickenMan - 07-01-2021

I actually have a 32k coreboard the has 1 chip in for memory (62256 - 32k) as well as a 27256 eprom that contains Basic, Wordbee & EDASM roms and a few other smaller support chips all on a standard Microbee 1632 Rev D coreboard.