Search found 27 matches

by VIP Quality Post
Mon Apr 13, 2020 12:26 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Wow! Between work and the plague, it took a while to get back to this. I found the issues. While I had the due diligence to check if my programmer was working fine, and my board was fabbed fine, I never looked at my EPROM adapter. I just got one off eBay a while back and assumed it worked. I found s...
by VIP Quality Post
Thu Mar 05, 2020 9:51 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Sorry I haven't replied in a few days, been busy with work. That looks like 60Hz that went through some kind of digital TTL buffer (thus the asymmetric 75% duty cycle). Check your grounding. That's interesting, I've never seen that before. I will check again this weekend. some decoupling caps might ...
by VIP Quality Post
Tue Mar 03, 2020 10:53 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

As an addendum, I see the oscillation on all channels of the EPROM that are connected to the 257s. The ones that are floating seem OK, or at least I haven't been able to find it on the scope (yes, I am using triggers)
by VIP Quality Post
Tue Mar 03, 2020 10:49 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Wow, just keep finding weird stuff. Maybe I bought some bad chips or something. I removed all the parts from the boards. I checked the EPROM again (still has correct data in all banks). I stuck it on a breadboard with the two '257s. With the 257 not hooked up, I can read the memory fine. With the '2...
by VIP Quality Post
Tue Mar 03, 2020 8:58 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

... And the ROM drives the data pins low / leaves them floating, even though you know it's erased (i.e. all $FFFF) and /G and /E are tied low? There's something Very Suspicious about that—that just doesn't make sense. I can't imagine you'd've made this mistake, but you haven't got the ROM in backwa...
by VIP Quality Post
Tue Mar 03, 2020 8:16 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

You said you measured the voltages on the ROM (not just the card edge) when it was in isolation? Have you tested whether low voltages are actually driven instead of floating (by e.g. comparing to the +5V supply instead of comparing to ground) ? You also said you tried tying the ROM's /G and /E inpu...
by VIP Quality Post
Tue Mar 03, 2020 7:24 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Here is my drawing.
by VIP Quality Post
Tue Mar 03, 2020 2:24 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Do you have a schematic? Photos of the PCB before/after assembly? I'll post mine when I get home from work today. I never looked at the SRAM behavior up close. I am thinking to remove the SRAM from the circuit and see what sort of behavior happens then. this sounds like a point where one asks "you ...
by VIP Quality Post
Mon Mar 02, 2020 11:32 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

Why not try powering the cart out of the SNES entirely? Provide +5, ground, tie /RD and /ROMSEL low, and measure voltages on the data bus. (edit: Oh, I see, the 1652 only has HPIB, not ethernet) Kind of a weird idea, but also makes a lot of sense. I set up my power supply and am not seeing anything...
by VIP Quality Post
Mon Mar 02, 2020 11:02 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

yes the Data bus lines. Can't you hook the analyzer up to OE and check it? Yup, I already had it hooked up to /OE. I previously had it (322 OE) connected to /RD but you can see from the trace it is being pulled low and nothing is going on the bus. I have it grounded now and I am still not seeing an...
by VIP Quality Post
Mon Mar 02, 2020 10:49 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

That generation of HP logic analyzers run X11 and HP/UX; you should be able to X-forward the display to another computer. I don't think the 1652 has it. The 1660/1700 series do, but the 1652 is an earlier age. "SYSCK", or whatever you want to call it, isn't a useful phase relative to /RD. You'll no...
by VIP Quality Post
Mon Mar 02, 2020 10:06 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

What do you mean by "them"? Are you referencing the data bus? I am thinking if there is something shorting the bus to ground that it wouldn't be able to read the $55 from RAM anyway. I agree that the ROM is not being enabled. I am going to try and jumper some PCB traces around to see if I can get th...
by VIP Quality Post
Mon Mar 02, 2020 9:51 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

OK, so there is something funny going on. I programmed another EPROM with FF in address $00FFFC and $00FFFD, just to see if I could look it up. I am not seeing that value at all. dummy data.PNG In addition, the timing analysis shows that RD is being pulled low fairly regularly, in step with the cloc...
by VIP Quality Post
Mon Mar 02, 2020 7:03 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

As you had issues with the address pins, I would double check the data pins as well. You can open the ROM in a hex editor and see what values it should read at those locations and make sure your logs match. I crossreferenced the ROM when I initially had this problem because that is what I thought w...
by VIP Quality Post
Sun Mar 01, 2020 9:18 pm
Forum: SNESdev
Topic: Boot routine/ bank selection?
Replies: 41
Views: 9135

Re: Boot routine/ bank selection?

The thing that's really stumping me is that it's not even trying to read the ROM for initialization, it's never pulling RD low. I can't seem to find any specific information on what the CPU is supposed to do between the reset vector and when it looks for code to read from the ROM, which is where it'...