My new project: Foozle11 A T-11 based SBC

[jockm]

Since the PCB is finished and I am about to send it out to be made, I wanted to share a project I am working on. It is a T-11 based single board computer, heavily inspired by leegleason's T-11 SBC. I have attached the schematics below.

The basic rundown is:

• T-11 CPU clocked at 6Mhz (7.5 Mhz standard oscillators seem a bit hard to find)
• 32K of ROM that can be enabled/disabled on the fly
• 512K of SRAM arranged in 8 banks of 65K
• A compact flash slot for storage
• Two W65C22S VIAs for IO. One port is used internally, and the other 24 are available to the user
• A FT245 USB UART
• A CPLD (ATF1504) for address decoding
• Up to two I/O Expansion Cards (well one header and two chip selects)

My goal is to get it working and then write a simple DOS for it (since it doesn't look like a standard PDP-11 and thus getting a standard DEC OS to run on it would be unlikely), or maybe port something like BKUNIX/FUZIX to it... or get distracted by something shiny and just put Forth on it lol.

Eventually this will all be up in a github repository, but I thought I would share the schematics and let people know, so I can feel a little pressure on me to keep going

 

[daver2]

Cheers,

I can only see sheet 1 of 4 though in the PDF file...

Dave

 

[jockm]

Cheers,

I can only see sheet 1 of 4 though in the PDF file...

Dave

DOH! Fixed in the orignial post. Thanks for catching that!

 

[saipan59]

Since the PCB is finished and I am about to send it out to be made, I wanted to share a project I am working on. It is a T-11 based single board computer, heavily inspired by leegleason's T-11 SBC. I have attached the schematics below.

The basic rundown is:

• T-11 CPU clocked at 6Mhz (7.5 Mhz standard oscillators seem a bit hard to find)
• 32K of ROM that can be enabled/disabled on the fly
• 512K of SRAM arranged in 8 banks of 65K
• A compact flash slot for storage
• Two W65C22S VIAs for IO. One port is used internally, and the other 24 are available to the user
• A FT245 USB UART
• A CPLD (ATF1504) for address decoding
• Up to two I/O Expansion Cards (well one header and two chip selects)

My goal is to get it working and then write a simple DOS for it (since it doesn't look like a standard PDP-11 and thus getting a standard DEC OS to run on it would be unlikely), or maybe port something like BKUNIX/FUZIX to it... or get distracted by something shiny and just put Forth on it lol.

Eventually this will all be up in a github repository, but I thought I would share the schematics and let people know, so I can feel a little pressure on me to keep going

Hi,
R1 should be 1K, not 10K. The T11 docs are very specific about that value (but I don't think they say why).
You need to ground XTAL0 (pin 23).

Pete

 

[jockm]

Hi,
R1 should be 1K, not 10K. The T11 docs are very specific about that value (but I don't think they say why).
You need to ground XTAL0 (pin 23).

Pete

Huh I got the 10K from... somewhere, but fixed and fixed. Thank you!

 

[jockm]

Side note: Foozle is a word from my familect, that came from mishearing the name of the animal Fossa from Penguins of Madagascar (no I don't have children, why do you ask?), and has become a placeholder name for projects. I have designed a handful of SBCs for processors new and old that have the prefix Foozle

 

[Dare]

512K of SRAM arranged in 8 banks of 65K

How does the memory banking work? Any thought of using an MMU like the 74LS612?

... or maybe port something like BKUNIX/FUZIX to it

Probably pretty straight-forward to port Mini-Unix to it. New CF disk driver plus a new console driver should do it.

 

[jockm]

How does the memory banking work? Any thought of using an MMU like the 74LS612?

Three pins of one of the VIAs are connected to A16-A18. There is an additional pin on that VIA that signals to the address decoder if upper ram should be mapped to the current RAM bank or to the ROM. That way the ROM can hold utility code and the like, and a small stub in ram can take the parameters to a call, enable the ROM, and call into it. I am planning on putting basic compact flash access calls, and maybe a port of Elm Chan's Fat Fs library in there, along with a simple bootloader.

I did consider using larger CPLD and implementing a MMU, but decided against it. I wanted a fairly straightforward and naive design. Part of the purpose of this project is to gain familiarity with the T-11 and PDP-11 ISA in general before I tackle a bigger project. This seemed like a good compromise for a first project

I do plan to build something like a PDP-11/Hack in the future so I can run off the shelf software; but wanted to understand things a bit better first. While I have a love of the PDP-11, my personal experience starts with the VAX (both MicroVAX and VAXStations).

Probably pretty straight-forward to port Mini-Unix to it. New CF disk driver plus a new console driver should do it.

BKUnix is an update of Mini-Unix/LSX to run on the Elektronica BK series of microcomputers. They had a PDP-11 compatible, soviet made CPU. It has the advantage of having been updated to use more conventional C syntax, rather than the v6 C of Mini-Unix.