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

[ChickenMan]

The Viatel ROM was the first one I swapped out initially as even if you do have the viatel mod or not, there is nothing to connect to so today its totally useless. This is where I eventually put my Defender ROM that can ONLY go in that position. I can make it available if your interested.

[CheshireNoir]

Thanks for the offer! I am interested. It may not stay there, but I'd like to try at least :-)

[ChickenMan]

Okay, have emailed it to you, give it a try and I'm interested in your results.

[someone]

I suspect more like a signature byte, I think the boot-up to the SHELL menu is too quick to do a CRC check on each ROM every time it boots up.

PS. Even though Self Test doesn't show PAKs 6, 7, 14 & 15 PC85 still checks for and will display in the full menu list, even PAK's 6, 7, 14 & 15.

The only one it will not display is Pak 10 which is reserved for the Menu expansion of SHELL.

Ernest

The first byte is a 0xC3 & checksum is only on the first 256 16 bit words of a PAK ROM so it is done very quickly.
The titles of the recognised ROMS are stored in the menu system; the original PC85 menu and PC85b have slightly different entries.

[ChickenMan]

As it says in the Engineering Notes

UPGADING TO PC85 version II
All coreboards, versions 8328-4 and 8328-6, will take 27128
EPROMs in the PAK locations. Some early PC85's had 8328-2
coreboards and these have to be modified to use 27128 EPROMs.

So I thought why not add something to the upper 8kb of Rom C, the Wordbee rom, PAK 0.  I burnt out a 27128 with Wordbee in the 1st 8k  and the Keyboard version of Survivor in the 2nd 8k.  Tested it in ubee512 and all works as expected, I hit W from the main menu and Wordbee starts.  Hit RUTURN from the Menu and now PAK 8 shows up, select it and Survivor starts.

   

So I now burnt out a 27128 eprom with the file and replaced my ROM C with it.  Powered up the PC85, select W form the Menu and Survivor starts   From the command Menu there is no PAK 8 and PAK 0 is listed as User rom.  I also tried it in my Prem PC85 with the same results.  Both have the 8328-4-03 coreboard.  Could it be something to do with the jumpers under the ROM, but I cant find any reference to them in the documentation.

   

[Ernest]

Hi ChickenMan,
The behavior you get is expected. The emulator correctly decodes the PAK 8 address, whereas the real hardware does not.

The problem is with PIN26 of the the "C" ROM IC15. From memory this pin is held to +5V and doesn't get the decoded signal for the upper bank as the "E,F,G,H & I" ROMs do.
So when you place a 27128 ROM in the ROM C position, due to PIN 26's being hardwired to +5V it selects the upper bank, hence you loose the WORDBEE selection. This is not a problem for the 2764 as that pin is NC.
Not having a MB8328 board myself I am not 100% sure PIN 26 is hardwired to +5V but from my research indicates that it is very likely.

Isolating PIN 26 from the +5V and connecting a jumper from PIN 26 to pin 1 of IC28 will solve your problem.
I can confirm that my modified MB1732 board which I have changed to run as a PC85b works fine with Wordbee in PAK 0 and Typing Tutor in PAK 8 locations.

PS, Very annoying that I can't see the picture of the rom_c.png in your post while logged in, I have to log out to see it. I would be nice to get rid of this software bug.

Ernest

[ChickenMan]

Thanks Ernest, I put the original Wordbee rom back in and PIN 26 reads +5v. So cut the 5v track going to PIN 26 on the solder side of the coreboard and connected it to PIN 1 of IC 28 as you suggested and bingo all is working. W brings up Wordbee from the main Menu now and I can select Rom 8 from the Command menu to get Survivor. So now have Space Invaders in top 1/2 of Rom E, RobotMan in top 1/2 of Rom I and Defender in all of Rom H so think I will leave it at that.

"The emulator correctly decodes the PAK 8 address, whereas the real hardware does not." I therefore read that as ubee512 doesnt emulate the real hardware correctly then.

As for not seeing the pic, can you see the Command menu pic a few line above it or not ? I've triple checked the Setup and Attachments are turned on for all, thats Guests, Members, Mods, Admin so seams Members are the only one where it doesnt work correctly. Will see if there is an update.

[Ernest]

Great to hear your success,
This is not the first time I have seen uBee512 not emulating a hardware deficiency, I have seen several examples over the years.

I have not been able to find a logical reason for the upper bank switching to have been left off this board design. The only thing I can speculate, is that the designers wanted to give locations of ROM A,B & C (IC5, 10 & 15) the ability to run mask ROMs 2564's and also 2532's / 2732's which therefore requires the +5V on Pin 26 (PIN 24 in the case of the XX32's).

Yes I can see the Command menu pic regardless of my logged in status.
They are both .png images, but the only thing I can see is that the Command menu pic is attached as a thumbnail and the rom_c is a full image attachment. However as I'm not fluent in HTML script I could be reading it wrong.

Ernest

[ChickenMan]

This is not the first time I have seen uBee512 not emulating a hardware deficiency, I have seen several examples over the years.
Ernest

Same here, my biggest concern is with CF images.  Images that boot in ubee512 and allow you to copy files to and from your PC HD but do not boot in real hardware.  While images that do boot on real hardware while they boot up in ubee512 but you cant copy files to and from them.  So for these I have to use the slow process of using a Gotek to transfer files on real hardware, doable but substantially slower.

My PC85 has Mask ROMs in A, B, C & D and its only Roms C & D that has 5v connected to pin 26.

Both pics in the above post were added in the same way and both should be thumbnails.

[Ernest]

CF's on Microbee hardware are a problem of their own. A CF card that works fine in one hardware system won't in another. Even just changing the Mainboard and keeping a Coreboard CF card combination will sometime work and other times not. Some brands of CF cards are more prone than others. My rule of thumb has been the slower and older types of cards work better than newer more modern cards.
I also use the GOTEK method for transferring files, as it is robust and straight forward but limited in capacity. I have not spent a lot of time working on uBee512 / real hardware interchange via CF card, as most of the time I can fit what I need to transfer on a single or two GOTEK floppy images.

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