6502.org

I stumbled by chance on this forum and was pleasantly surprised to see that the 6502 is still alive and well (apologies to all those afficionados who believe that the 6502 was the best thing ever invented - I thought so too).
I worked with it in the late 70's , early 80's when it was all the rage (especially in the UK.) Maybe some of you remember the Rockwell AIM65 !?
Anyway my purpose in writing was just to say that I developed an In-Circuit-Emulator for the 6502 in 1982, and though it worked well I didn't get round to marketting it (which I think now was a big mistake) . After that Ideveloped ICE's for Z80 , 8086 , 8085 and other CPU's.

However I am happy to offer the design to anyone who is interested. It would only be in its raw form - full schematic - and I may be able to dig up some construction notes for it which I wrote at the time.

Incidentally I had it running under control of the old BBC microcomputer, using the main expansion port. It could be fairly easily modified to use a 6502 general purpose control board with say a USB interface for a PC etc.

The design has been gathering dust now for nearly 30 years so any takers are welcome,

regards,

David Kelly

Hello, David! I'm delighted that you found our group. Certainly your sentiments regarding the 6502 make you welcome here!

The In-Circuit-Emulator sounds like a fascinating project, and there are many here who would be interested in how you pulled it off. But the documentation is probably on paper, and would require considerable effort to scan into electronic form. So to begin with perhaps you could provide us with an overview, either as a written description or a block diagram or both. Would I be correct in assuming that the design includes an actual 6502 chip, surrounded by an added layer of hardware? Then of course there'd also be the interface to the BBC host computer, and some software on that end... All in all, a very tidy little project! We'd love to hear about it.

Cheers,

-- Jeff

Hi Jeff ,
nice to hear from you. Your observations regarding the H/W details were spot-on. At the heart of the ICE is a 6502 executing 6502 M/C so giving full-speed emulation.
The system also was designed to provide single-step execution of IRQ's , including NMI's (quite a challenge to pull of as I remember).

If I were to consider taking this design to fruition again (minus the BBC Micro of course), I would probably use an AVR chip via a USB port to a PC . This would also allow me to clean up some of the slightly cumbersome control logic driving the 6502 functions.

I will proceed to put together the documents you requested and let you have them as soon as I can.

Once again thanks for your considerate response and look forward to 'interfacing' with you,

regards,

David Kelly

Things have changed a lot in the last 30 years, and we have access to some truly miraculous technology today. But of course the technology of 30 years ago also seemed miraculous at the time!
OK, but there's no pressure, so proceed at whatever pace you find comfortable. And don't feel obliged to provide a lengthy, polished document. You might begin by noting what the device is capable of -- similarities and differences compared to a Logic Analyzer, for example.

-- Jeff

Would bew a quite useful tool as an in circuit repair and design tool....

I have published the main details for my 6502 ICE design on a web page accessible at :
[http://www.wix.com/davidkel06/davesprocessordesigns]

Once again , thanks to Jeff for some helful tips and some good down-to-earth advice.

Hi, I've been reading about the 6502 recently and just came across this thread. I wanted to know what an In-Circuit emulator can do. I've been working with TI DSPs for quite sometime now and haven't come across the idea of in-circcuit emulator probably because of my involvement in commercial R&D projects instead of academic R&D. @Nightmaretony, can I ask how it may be used a circuit repair and design tool?

Unfortunately, Nightmaretony can't answer, we lost him late last year. Someone else may chime in, however.

deniz:

After removing the 6502 from a faulty CCA, the in-circuit emulator can be used to excercise the CCA. It's debugging capabilities allow testing at a level of detail that is not generally available using a monitor program. I used TI DSP extensively in the past and I was not aware of any in-circuit emulators. Could you be referring to in circuit debugger using JTAG or similar interface. In my experience, the level of debugging available with these functions has never matched the capabilities of a good in-circuit emulator. I am very appreciative of the on-cip debugger capabilities of my ARM processors, but I would still prefer a good 8051 in-circuit emulator than an on-chip JTAG debugger.

I'll chime in...

An in-circuit emulator is usually a hardware device which:

1) Replaces the processor in the target system and emulates it. This requires the target system to have a socketed processor which can be removed, and a plug from the ICE is plugged into the socket.

2) Allows debugging of code running on the processor using various hardware features. This usually includes but is not limited to:

a) Hardware breakpoints triggered by code execution (instruction fetch)
b) Hardware breakpoints triggered by data memory access. These may be triggered by read or write
operations or both, and may have selectable mask bits on the address or data bits.

In-circuit emulators may or may not have:

1) Source-level debug capability. The 6502 ICEs I used (American Automation aka Arium, Intelligent Designs, etc) usually did not have source-level debug capability because there was no standard symbol format for 6502 executables.

2) Ability to load executables into the target. The ICEs I used did not, because the target system ran code from ROM, and the ICE had no ability to write to the ROM. We had to use a separate ROM emulator, such as a Grammar Engine ROMulator.

Toshi

One implication is that you can debug the I/O and other hardware portions of your actual board. Even if the software is perfect, there can be hardware problems on the board which the ICE can help you figure out.

Hi all --

I'm looking to revive this topic for a moment. I happen to have a need for something like this for a project, and I tried to email David about the higher-resolution schematic (his Wix site has the low-res one) but the email bounced. So I thought I'd ask if anyone knows if he's still on-list or if they have the schematic.

He also references other designs, and I happen to need one for the 8086 (for a VGA board project for an S100 machine).

Anyway, thanks!

Rich Cini

You could try sending him a PM (if you haven't already). Then I suppose there's LinkedIn, other social media etc...

I started with an email from his site but I will PM him here also. Thanks.