A little PCB for my PC85

CheshireNoir · 13-12-2021, 12:22 PM

Hey Folks,
I have an evil plan. I'm going to make up a small board to take an M27c2001 ROM, a hex rotary encoder and a couple of pull up resistors.
The idea is you can slot it into one of the spare sockets on a core board, and you can switch out up to 16 x 16k ROM images or 32 x 8k ROM images.
I like the idea of being able to install a stupid number of ROM enabled games into one socket, and switch between them simply by powering down, turning a dial and powering back up, then calling the appropriate PAK for that slot.

I want to try this, just to see if it'd work!

First draft is here: https://github.com/cheshirenoir/BeeMultiRom

Feedback gratefully accepted. I've already received feedback on another forum about making some of it SMD to see if I can make it fit in all sockets. (No idea why you'd need that many ROM images. TBH I don't know if I'll be able to fill all 32 x 8K slots as is :-D ) I'm planning on using turned pin posts as they seem to be the best compromise of strength without putting too much stress on the sockets.

I won't get a chance to get the PCBs ordered for a month or two, so I'll think about what tweaks I could do. I'm already contemplating removing the rotary dial from the board so it can be extended out of the case. I was planning on making one board with it on board for testing and then just wiring to the pins for the final.

Oh, and it's CC-BY-SA so anyone who wants to fiddle has the full Schematic and PCB in KiCAD and my explicit permission to go wild. It's not like it's a complicated circuit.

Cheers!

Chesh

***ChickenMan*** · 13-12-2021, 05:23 PM

Sounds like a good idea to me and worth the effort to try it out.

Most of the "better" bee games would fit into a 16k space, not that many for 8k so I would stick with 16 x 16k. But my favorite, Scavenger, is even bigger at 23k.

Ernest · (This post was last modified: 13-12-2021, 06:52 PM by Ernest.)

Just bee aware not all games are designed to run from the PAK location, so will need to have a relocation program run to move it into normal memory to run.

Ernest

Where did you find a source of "Turned Pin Posts"?

Ernest

***ChickenMan*** · 13-12-2021, 08:02 PM

As Ernest said, most of the "better" *.BEE games do not load at the default 0900h address and none of them load & run from C000h. But most/many of the games have had a routine added at the start or end to allow loading at Basics default 0900h and them move the code to its right position and jump to its start address, but not all. So you really need to study the code of each game at the start and end to see what you need to change the code to run from a PAK position. Also, read the eprom_programmer_and_64k_rom_pak_instruction_manual.pdf manual that explains how to setup a 16k file in the 2 x 8k parts.

someone · 13-12-2021, 08:12 PM

IC's often fall out from machine pin sockets thus many designs use an IC retainer clip or zip ties.

Ernest · 14-12-2021, 08:07 PM

(13-12-2021, 08:12 PM)someone Wrote: IC's often fall out from machine pin sockets thus many designs use an IC retainer clip or zip ties.

Thanks someone, unless you are bouncing around in the back of a car, good quality turned pin sockets grip well enough for use in the Microbee.
However, I was asking about Turned Pin Posts - these are needed if you need to plug in a daughter board into a Turned Pin Socket (as is the case here), normal headers are useless for this.

Ernest

someone · 14-12-2021, 09:52 PM

(14-12-2021, 08:07 PM)Ernest Wrote:
(13-12-2021, 08:12 PM)someone Wrote: IC's often fall out from machine pin sockets thus many designs use an IC retainer clip or zip ties.

Thanks someone, unless you are bouncing around in the back of a car, good quality turned pin sockets grip well enough for use in the Microbee.
However, I was asking about Turned Pin Posts - these are needed if you need to plug in a daughter board into a Turned Pin Socket (as is the case here), normal headers are useless for this.

Ernest

Machine Pins comprise of a turned pin with an internal spring insert. Mill-Max & Samtec are leaders in this field. Have a look at their web sites for compatible mating headers. Be aware that the come in a large range of different configurations. When one cannot rely upon the spring pressure of the machine pin socket for retention, often accompanying retention screws and screwlocks are used.

mjelic · 02-03-2022, 09:20 PM

(13-12-2021, 12:22 PM)CheshireNoir Wrote: First draft is here: https://github.com/cheshirenoir/BeeMultiRom

Feedback gratefully accepted.

Cheers!

Chesh

Just a thought, but whenever I've made a board in KiKad, I always make a 3D render of it and put that in the Readme.MD file on my github.

https://github.com/Gonzo-XIII/TEC-1_Hard...C_Expander

Makes it easier for people to visualise how it connects together.

CheshireNoir · 03-03-2022, 12:20 AM

Well the boards are in the tender mercies of Australia post right now...
I'll let you all know how it goes.

Chesh

CheshireNoir · 19-03-2022, 12:57 AM

Finally got the boards back last week. Spend last night building up a composite ROM and... It works! It actually works!
I have it in the ROM H position, and it'll even work with 16K ROMs in that slot like Defender.
The biggest issue I hit was not really knowing how to convert more software to work as ROMs. After all. this gives me slots for 16 x 16k ROM or 32 x 8K ROM. That's a whole lotta ROMs :-)

I've updated the Github with the Gerbers.

Chesh