Upgrading a Microbee PC85 to a PC85b and adding extra Game ROMs.

[ChickenMan]

ROM D (from my notes) would be the NET ROM (IC 20) this is able to have 32Kb or 64Kb/128Kb ROM's fitted, so power to PIN 26 of this socket is required to allow the 32Kb ROM to be powered (PIN 24 of this ROM). To run a xx64 would work fine without MOD but the Circuit shows the possibility of using a 27128. Once again the lower half of the 27128 can't be accessed without changing the link going to PIN 26 of this socket, which by default is connected to +5V. Changing the link enables the switching between the lower & upper banks.

I don't know why they didn't do the same for ROM C (IC15)?

Ernest

Yes Rom D is the NET Rom and currently has 5v applied to Pin 26 via the 3 small points just below the rom. Point 33 is connected to the 5v rail. 34 is connected to Pin 26 of Rom D & to 33 and 35 appears to be connected to Pin 1 of IC28.  So cut the small link between 33 & 34 and bridge 34 to 35 would obviously allow a 27128 rom to be inserted in Rom D.  Not sure how you would ever access the upper 1/2 of a 27128 though.

[Ernest]

PAD 35 shouldn't be connected to IC28 PIN 1 as IC28 is only associated with bank selection of the PAK ROM's residing at C000h.
PAD 35 should go to IC 26 PIN 5 which is the upper bank selection of a 27128 (if fitted) to ROM D location (NET ROM).

This bank selection uses a little known function of the Z80 where it places the contents of the A register out onto the upper Byte of the Address Bus when doing an INPUT command from a Port. After reset it is always reset to the first 4KB (32kb) 

Chapter 4 - Coreboard description in the Technical Manual gives an example of how to access the four 32kb banks of the NET ROM location.

LD A,2          (note this is either 0,1,2 or3 depending on which bank you wish to launch, 2 & 3 are the upper half of the 27128 EPROM.)
IN A,0Ah       (Port #10)
JP NET

The PC85 uses the two lower banks 64kb for TELCOM, Calculator, Self Test & MONITOR (I believe it is a different monitor to the one in the WORDBEE ROM). 
However I have yet to find a program designed to go into the upper 64kb of the NET ROM location.
Just about any 4KB programs that are compiled to run from the E000h location and don't need access to any of the other programs listed above.

Hope this helps.

Ernest

[mjelic]

Newbie/Dumb Question time:
This is what I would like to have on my Microbee: A bunch of (or one big) set of ROMs that has the software I want to run on there, being easily accessed from a menu.

Mine is the 128k 3.5" diskette version, which is lovely for saving files... But I didn't want to have to load any games or software (all I really want is an Assembler) from the disks. Is what you have done even possible on my Bee? I've opened it up and it doesn't look like I have any more than a single ROM socket. And when my machine boots up, there is certainly no pretty menu, just a non-blinking cursor at to left. Rather sad.

Did I buy the wrong Bee for my needs?

[ChickenMan]

All the above is for ROM based Bee that you would normally load a game in via Tape, a slow process really.

No, you have one of the best and most useful Bees made, but what you need is a Gotek to replace your Floppy drives. You just copy the DSK floppy images to a USB key, select the floppy you want to boot. Most of our games disks are fully Menu driven also, just select what you want to play. Best is a Gotek with LCD screen and rotary controller with FlashFloppy Firmware, about $80 off ebay.

[CheshireNoir]

Mjelic,
I'd happily trade one of my SRAM / ROM Microbees for your DRAM Microbee, but I agree with ChickenMan. The Gotek is probably the way forward for you.

(I've ordered PCBs for a multi ROM switcher for my PC85. Will report back how it goes :-D)

Chesh

[mjelic]

Mjelic,
I'd happily trade one of my SRAM / ROM Microbees for your DRAM Microbee, but I agree with ChickenMan. The Gotek is probably the way forward for you.

Well... I come from the TEC-1 world... We never had these fancy floppy disks and we barely even had tapes to save our data off.  And what we do currently is use an assembler on a PC, write the resulting OBJ file to a NV-RAM and then pop it into the TEC-1 to test it.  Not exactly a fast way to develop. The TEC-1 also doesn't have a full sized keyboard (only a hex keypad), nor does it have a screen. It has six 7 segment displays and if you're lucky, a 2 line x 16 character LCD.

So, having a ROM based Bee would be a nice step up for my needs. I'm pretty sure I saw a Bee that had like 5 ROM slots? As long as a couple of those ROMs could hold a game like Defender and Zork (lets face it, I wouldn't be playing that often anyway) and the other an Assembler and maybe a disassembler, I would be set.

But, I'm just kind a realising... Do the ROM Bees not have ANY ability to save data other than tape?? Hasn't there been someone develop something that can go into the 50 pin expansion that has a CF card or SD card or USB stick?

[ChickenMan]

Sorry to say but programs like Defender and Zork are WAY to big to fit into even a 16k Eprom, ZORK is 75kb with a 9kb loader big which is one of the smallest Infocom games. Minizork is 51kb with a 8kb loader.

There are rom external boards that plug into a 50 way (that needs fitting) but again they only take 8kb roms and for the early Series 1 units. There is no floppy or HD controller onboard these units, so yes one could be designed I'm sure to handle a CF or SD or USB to plug into its 50 way port with boot rom in place of the Telcom (Network) rom maybe. So there lies a challenge

Your system has a Floppy controller onboard, just plug a Gotek in and you can be running what ever within seconds.

[mjelic]

Sorry to say but programs like Defender and Zork are WAY to big to fit into even a 16k Eprom, ZORK is 75kb with a 9kb loader big which is one of the smallest Infocom games.  Minizork is 51kb with a 8kb loader.

There are rom external boards that plug into a 50 way (that needs fitting) but again they only take 8kb roms and for the early Series 1 units.  There is no floppy or HD controller onboard these units, so yes one could be designed I'm sure to handle a CF or SD or USB to plug into its 50 way port with boot rom in place of the Telcom (Network) rom maybe.  So there lies a challenge

Your system has a Floppy controller onboard, just plug a Gotek in and you can be running what ever within seconds.

Ah... I see... How big is EDASM?



Going by the MSPP, the PC85 Premium looks perfect for me... Except no way to save files off without tape. Yuk.



Look at this thing of beauty.

   

[CheshireNoir]

Alas, for some reason I cannot view it.
There are Floppy drive adapters for the SRAM systems that do plug into the 50 way connector. At that point you could plug in a Gotek to save to USB.
You're still limited to 32k :-D

Chesh

[mjelic]

Alas, for some reason I cannot view it.
There are Floppy drive adapters for the SRAM systems that do plug into the 50 way connector. At that point you could plug in a Gotek to save to USB.
You're still limited to 32k :-D

Chesh

Hmm, OK... Have you got a link to these floppy adapters? And I assume there is a ROM that goes with it or such?

The TEC-1 has 2k by default on it... 32k is plenty for what I want to do.

So, do you have a Premium PC85?