Recent content by Uniballer

And of course, sometimes, on some models (the Good Ones), you also care about data space as distinct from instruction space (i.e. KDSAR5).

If you only need local then this works: Viking Electronics DLE-200B Two-Way Phone Line Simulator I used it back in the day for testing demand-dial routing software. I have had similar issues with VOIP for fax, but have not tried old dial-up modems at all.

Yes, you see that on the 6800 as well, but without VMA on the spurious cycles. E.g. assertion of index register contents (no VMA), followed by index register plus offset without carry (no VMA), followed by the proper indexed address with VMA. Kinda interesting how much info that gives about...

Just to be sure we are talking about the same issue: cycle 4 of CLR extended, and cycle 5 of CLR indexed, actually reads the operand address with VMA asserted, just as with all of the other read/modify/write instructions. You are correct that VMA is not asserted in the following cycle, and then...

But the 6800 CLR instruction does an obscure (but real) read with VMA asserted prior to the expected write. So the operand read cycle in CLR is especially insidious, and thus worth remembering (but maybe not for over 40 years).

Yeah, some I/O devices do things like clear interrupts based on a read that you wouldn't want to do by accident. No. I think it was the data book @cjs linked to. Personally, I never found Leventhal's style appealing; also he tends to muddle some details (e.g. referring to the PS V bit as O)...

Either looks OK to me. I did a bunch of 6800 code at one point, and I recall that CLR <addr> does a read before writing 0, and that can cause issues if you are not aware of it. I recall that we had a book that contained a cycle-by-cycle description of all instructions (from the data sheet?)...

TTL level serial data is inverted (RS-232 inverts it and changes levels). First will be a start bit (TTL low). So you reading 0101000 is Start bit, 0, 1, 0, 1, 1, 1, and the stop bit is TTL high.

Local hardware store (TrueValue at the time). Nothing too exotic. I probably took an unused (aka not yellowed much) drive bay cover in with me and found a close match.

I actually looked for it before posting. The wife said she painted a green plastic flower pot with the rest of it, and then tossed the empty can. C'est la vie. I didn't ask why she wanted a flower pot the color of a vintage PC case ;)

When I wanted a retro looking ATX case I spray painted an ebay Antec 300 with Krylon Fusion (don't remember the exact color, but it looked good).

Different real PDP-11 models might handle this situation differently. It is pretty hard to say that this is wrong behavior on simh's part because there was never a complete functional spec written for the PDP-11 (the VAX spec is far more complete). What trap did the simh PDP-11 take? Why was...

At the time I was doing a bit of custom surface mount stuff and also recapping some power supplies and motherboards. I got pretty fed up with the Weller and Hakko FX888D that I had and heard about the FX951 (probably on EEVblog or someplace like that). I went for it, but made sure I was...

Somebody gave me a big old 100 watt soldering iron, no idea what brand, when I was about 12. It took a while to heat up all that metal, but it held heat like crazy. I got good enough with it to solder transistors without frying them... I don't know what happened to it. In my late teens I got...

My first computing experiences used a DECwriter II with an acoustically coupled modem to the BOCES IBM 370.