New open source, expandable 8085 Single Board Computer ecosystem - Page 1
Forum section: electronics / general

author: Ccandrews
author_rank: Contributor
timestamp: March 17, 2020, 04:31:41 pm
content: Hi allTypically I am pretty happy playing with vintage hardware, but a few months ago I suddenly had the urge to revisit my youth and build from scratch.I felt the need to go back to my favorite processor and update the first 8085 single board computer I wire-wrapped decades ago while working on an electronics research project in college. Now I realize there are currently some very well designed and nicely implemented 8085 SBCs out there, but I wanted something different and, specifically, something closer to my design back then.Overall, it is a backplane with individual cards akin to the MIL MOD8, STD bus, or any of a dozen '70s style systems that were trying to keep up with a changing world.I have the SBC completed and a couple of versions tested so I have released the build files for version 1.0 of the backplane and version 1.1 of the SBC. Sometime in the next week or two, I will be mostly through testing my v1.0 cassette interface board and bus monitor. Next up is a Remex paper tape reader interface card.I have some of the projects on hackaday and have created an SBC-85 websitehttp://SBC-85.com. As I get designs tested, I am making the build files available for others that may have a similar interest.I am pretty excited about this project which has been a great deal of fun and wanted to share with other 8085 diehards.RegardsCraig

author: ebastler
author_rank: Super Contributor
timestamp: March 18, 2020, 01:22:31 pm
content: Nice!Your design seems like a bit of a hybrid between a single-board computer and the old bus systems. The '70s systems had CPU, RAM, EEPROM... on separate cards, and had the full data and address bus routed across the backplane, right? In contrast, your design seems to have a complete SBC on one board, including some peripheral interfaces.Do you have plans for additional boards? (Which ones?) Does the backplane provide direct access to the address and data bus, or have you chosen a different approach there?

author: Ccandrews
author_rank: Contributor
timestamp: March 18, 2020, 04:01:14 pm
content: Thanks, you are correct about the design. It is basically a SBC that can be supplemented with additional cards. The demultiplexed address, data, and all other 8085 signals are on the backplane. The SBC works by itself or as part of a system.....Think of a 100mm square version of multibus.I have the SBC and backplane done, finishing up a cassette interface board software and a paper tape interface card. Those will probably eventually be combined into one card also with a USART if room. Have a pad-per-hole type protoboard and version 1.1 of an extraordinary bus monitor in the mail from the PCB house. A couple of memory cards on the drawing board for the next PCB order.The project is documented on hackaday and the project website SBC-85.COMOther cards to come as time permits. Any suggestions?Craig

author: woofy
author_rank: Frequent Contributor
timestamp: March 19, 2020, 11:23:57 am
content: Nice project, I like it.Just subscribed to your channel too.Are you self hosting SBC-85.COM? its very slow to load but gets there ok.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 19, 2020, 03:37:53 pm
content: Sorry if the question is silly (especially since this is Vintage computing here, so that could be enough reason), but is there a specific reason to choose a 8085 rather than a Z80? Although compatible, I thought the Z80 was an improvement on several levels?Again the choice of 8085 may just be for its own sake, so if it is, that's fine. If OTOH there would be a specific benefit of choosing a 8085 over a Z80, I'd be interested to know, as I haven't worked with either in a long time.

author: Ccandrews
author_rank: Contributor
timestamp: March 19, 2020, 03:43:06 pm
content: Quote from: SiliconWizard on March 19, 2020, 03:37:53 pmThe 8085 lived a much longer life than the z80 because of its use as an industrial controller. So while those familiar with consumer type of computers will be more familiar with the z80, those more familiar with industrial computers will be more familiar with the 8080 and 8085. The hardware interrupts and serial port gave the 8085 great stand-alone capabilities.But the real reason is that the 8080 and 8085 were my first loves and one never forgets.

author: Ccandrews
author_rank: Contributor
timestamp: March 19, 2020, 03:47:03 pm
content: Quote from: woofy on March 19, 2020, 11:23:57 amThank you!The SBC-85.com site is hosted on the cheapest hosting plan at hostgator.com. I expect they have 1000 of us on the same machine, but this is a low budget project.

author: rrinker
author_rank: Super Contributor
timestamp: March 20, 2020, 12:55:19 pm
content: Quote from: Ccandrews on March 19, 2020, 03:43:06 pmI dunno about that - variants of the Z80 are still being sold and in use in new products today.

author: SiliconWizard
author_rank: Super Contributor
timestamp: March 20, 2020, 06:01:38 pm
content: Quote from: rrinker on March 20, 2020, 12:55:19 pmTrue. Z80 chips in several variants can still be purchased from major distributors - still current devices!The Z80 also had DRAM refresh and other niceties (I think for instance the famous LDIR instruction was Z80 only?), so it was more adapted to computers with larger RAM needs at the time. Many if not most CP/M computers were Z80-based AFAIK.OTOH, the 8085 had an embedded UART and a bit more sophisticated interrupt controller than the Z80 (IIRC).

author: Ccandrews
author_rank: Contributor
timestamp: March 20, 2020, 06:07:42 pm
content: Boy, if you start counting variants this becomes a much tougher game to play and to know who wins. If you include variants and derivatives, my money is on the 8052 class.Maybe someone will make a Z80 SBC for this system.