TF536 + 68000 relocator and ROM board project.

[PhilC]

Forgot to mention I'm using EmuTOS so I can boot from HD

[stephen_usher]

Do you have extra power going to the TF? I do, via the relocator board. I replaced the capacitor next to the accelerator socket with a right-angled jumper and soldered the capacitor underneath.

I'm running TOS 2.06 from the (upper half) of the ROM. (And can boot from ACSI surprisingly.)

[stephen_usher]

See the problem with trying to fit the keyboard....?

IMG_2058.JPG

[PhilC]

Ok, I've been looking at track lengths etc for the lwct hand socket and having just seen the keyboard problem I've been thinking of where else things could go.

What do you tbink of this layout suggestion @stephen_usher ?

20201012_212200.jpg

I also noticed that the rom lines don't go to each socket in parallel but some to one and then some to the other, meaning track lengths can vary quite a bit on the address bus?

[derkom]

I also noticed that the rom lines don't go to each socket in parallel but some to one and then some to the other, meaning track lengths can vary quite a bit on the address bus?

8 MHz clock means a 37 meter wavelength. I really doubt track length variations are going to come into play here.

I seem to recall something about 10% of a wavelength being the place where you start to see problems, and certainly nothing on any reasonable size board is going to come close to that at 8 MHz. :)

[PhilC]

@derkom no arguments there but just thinking the circuit should be the same between the two sockets and the 74ACT157 and that my TF536 at least, works better in the nearer socket.

[exxos]

Lengths of tracks cause more ringing/oscillations the longer they are. Also they can couple to other tracks, such as gnd fill, which adds a few pF capacitance, and with the longer track lengths, you just built a oscillator. You have to use 2.2K bus resistors to help combat it all.

[stephen_usher]

I've just been using the oscilloscpe. Very interesting spikes on the /RESET line. On the 68000 socket I'm getting them at 60Hz and on the Accelerator at 230Hz.

The power and ground are quite noisy too, unsurprisingly. On the Mk.II board I've been starting to design I've increased the power traces to 6mm (any more and the autorouter fails).

The address and data lines look a little bit noisy but not too bad. AS from the TF is only 3.3V so could probably do with buffering onto the TTL bus.

The CLK line looks good on both sockets.

Oh, and the floppy doesn't work properly at the moment.

Anyway, I've run out of time tonight, I'd better pack up.

[exxos]

You need to use power planes for this stuff. If your just routing a power "track" its going to be nothing but headaches.

EDIT:

https://www.exxosforum.co.uk/atari/last/16mhz/index.htm Scroll down to March 10, 2015

[stephen_usher]

Hmm.. that would mean going up to a four layer board, which increases the costs hugely.