Tag: Jade

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8085/86 Getting Started

Posted on by Graham

This machine is a reconstruction of a hobbyist built machine from the early eighties. It came to me in pieces in amongst a lot of other gear, so it wasn’t obvious to me that there was a complete computer there at all.

I had already rediscovered a Cromemco based computer which used half a dozen of the 29 S-100 cards that i’d received. I also had a rack, some 8″ drives, and a lot of 8″ disks which i had previously imaged.

Many of the disks were labelled as being Jade, and there was indeed a JADE DD Floppy Disk Controller amongst the cards. There were many more disks that used the JADE format.

There was also a Versafloppy II Floppy Disk Controller card, for which there were also a number of disks.

These were all CP/M disks so i was looking for a 8080, 8085 or Z80 processor board. The candidates were a Cromemco SBC which wasn’t a great fit with CP/M or a CompuPro 8085/88 CPU card which would work.

I also expected there to be some I/O and a card for a boot ROM. And RAM of course. There weren’t a lot of clues from the cards themselves.

Fortunately there was a disk labelled “Jade System BIOS Development which contained some assembler files for the CP/M bios and the boot ROM. At this point, i ruled the Versafloppy II out.

The boot ROM code had some comments identifying key components (8251, 8255 and 8253) on a W/W card. Once i found the card with that combination of components, i realised that W/W stood for wire-wrap. It was a hand-crafted board. It also has a speech synthesiser chip!

Looking at the chassis, i could see that the wires dangling from the back panel married up with empty sockets on the board.

A little while later i realised that there a couple more ports which may belong to this unidentified card:

It has a real-time clock on it.

I had several memory cards that could potentially be used, but given that the CPU card is capable of addressing more than 64k, i started with an Intersystems 256KDR.

This card is probably overkill, and i may swap it out in the future.

I do have an EPROM card, but it is made for 2708 EPROMs which i can’t program at present – i would need a new programmer.

Instead, i built a new card using a modern S-100 prototype card.

These cards for the basis for the system.

Jade Double D FDC

Posted on by Graham

The Jade Double D is notable for being an intelligent floppy disk controller. The onboard Western Digital FD1791 FDC chip is controlled by a Z80 processor. The CPU communicates with the DD through a 1kB window.

Although the card includes a processor and 2k of RAM it has no ROM. Instead, code must be injected by the CPU card. The code is embedded in the CPU boot ROM.

The boot code assumes that the window address must be set to F400. The jumpers were already correctly set.

This card supports 5.25″ drives on a 34 pin interface or 8″ drives on the 50 pin interface. Eventually i will use 8″ drives with this machine, but in the short term i just wanted to use a couple of goteks (with Flashfloppy).

The images that i wanted to use are from 8″ disks. These work fine in the gotek but because the gotek uses the 34 pin interface there were a couple of residual issues. There are a some signals expected by the boot ROM and the CP/M BIOS for the 8″ drives that are not on the 34 pin interface.

The first is the RDY signal which is supported by Flashfloppy on pin 34. This requires a link on the DD from pin 34 of the 34 pin interface to pin 22 of the 50 pin interface.

The second is that an 8″ drive can detect whether a disk is single or double-sided – the index hole is in a different location. For this, i added a switch to assert or negate the SIDES signal depending on which image i had loaded. I later copied all of the single sided disk images to double-sided disk images to make things a little simpler.

This card had a couple of hardware issues. The first was two shorted tantalums. The second was that, for whatever reason, two sockets had been butchered, and the chips soldered to the socket pins.

I replaced the sockets and devices.

8085/88 First Boot

Posted on by Graham

The cards were popped into the rack, including a partially tested EPROM card with a boot ROM programmed using a file from one of the 8″ floppy disks.

The source showed that on start-up the first serial port to receive a space character would become the console and offer to boot from the Jade DD.

The boot ROM source indicated a serial port speed of 9600. I used an IBM terminal setup accordingly.

I started with a CPU, EPROM, and I/O cards and proceeded to discover the various mistakes i had made with the EPROM card!

Once i could see that code was being read from the EPROM i added the RAM board and the Jade Double FDC. I could see data coming out of the UART, but it wasn’t making it to the terminal and that was because a shorted tantalum on the Jade board had blown the -12V fuse.

Once repaired, i got the boot screen.

I hooked up a couple of goteks and on the second image it booted.

Credit to the original builder/owner/operator.