Re: [Simh] ALTAIR thinko?
On Mon, Feb 2, 2015 at 2:42 PM, Dell Setzer dset...@panix.com wrote: Probably folks back then were used to octal from having worked on minicomputers (like DG or DEC). I've forgotten that MIT's had grouped the switches in threes on their panel like the PDP-8 and PDP-10, and PDP-11. But you are right, that was the way DEC had done it for years. So I think it depending where/hpw you grew up. But you're right, it if you came from the DEC world, you probably were used to using octal from that 12 and 18 bit heritage. DEC did not really switch to hex notation until the 32 bit Vax. If your first assembly machines was System 360 is the like, you probably learned hex. Because I came up working on both DEC and IBM systems at the beginning, I sort went both ways (was schizophrenic??). When I wrote C code (like drivers) I found I always prefered hex for bit manipulations/masks in registers or results like CSRs or memory reads, but since DEC published address in octal, assigned pointers in octal - until the Vax. As for the micro's in those days, I tended to use hex exclusively in assembler and C, since that's what Intel (or Moto or MOS Tech) had defined in their architecture book. In 1975, I could not afford a MITs machine [I still have my copy of Pop 'tronics through) although one of my friends got one for his birthday that summer with a whole 256k bytes of memory [and I remember us drooling over it]. By late '77 I did manage to score a KIM-1 with 1K of ram (which I still have) -- FYI the KIM-1 it was purely hex. Clem ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
[Simh] ALTAIR thinko?
I've never seen an ALTAIR (beyond the Popular Science cover!) or used the emulated simh version, but I was reading code for edification and came across this statement in altair_cpu.c: 3. Non-existent memory. On the 8080, reads to non-existent memory return 0377, and writes are ignored. In the simulator, the largest possible memory is instantiated and initialized to zero. Thus, only writes need be checked against actual memory size. This looks like boilerplate copied from other simulators. Sure enough, later on, I find: for (i = MEMSIZE; i MAXMEMSIZE; i++) M[i] = 0; However, if the statement above regarding 8080 behavior is correct, and I have no idea if it is, shouldn't that line be: for (i = MEMSIZE; i MAXMEMSIZE; i++) M[i] = 0377; to preserve accuracy of the simulator? FWIW, Scott Bailey scott.bai...@hp.com ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] ALTAIR thinko?
On Mon, Feb 2, 2015 at 10:16 AM, Bailey, Scott scott.bai...@hp.com wrote: Non-existent memory. On the 8080, reads to non-existent memory return 0377, and writes are ignored. That was definitely true and how the HW worked [although the comment should have been 0xFF or actually $FF in Intel syntax - since the 8080s were defined in hex not octal like PDP-11s). There was no non-existent memory trap for the bus, so the HW read the data back as 0xFF because of TTL floating to high. I do miss the Altair and Imsai machines in a strange sort of way ;-) Clem ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
Re: [Simh] ALTAIR thinko?
Hello! Would the Octal reference for $FF be used because one of the authors of emulator would be more familiar with those terms from working with the one for the PDP-11? I've seen the crowd courtesy the VCF and have a box here who's waiting to be restored. Oddly enough I came within a big something-else to own one (an Altair or IMSAI or the Heathkit version) a long time ago. - Gregg C Levine gregg.drw...@gmail.com This signature fought the Time Wars, time and again. On Mon, Feb 2, 2015 at 10:40 AM, Clem Cole cl...@ccc.com wrote: On Mon, Feb 2, 2015 at 10:16 AM, Bailey, Scott scott.bai...@hp.com wrote: Non-existent memory. On the 8080, reads to non-existent memory return 0377, and writes are ignored. That was definitely true and how the HW worked [although the comment should have been 0xFF or actually $FF in Intel syntax - since the 8080s were defined in hex not octal like PDP-11s). There was no non-existent memory trap for the bus, so the HW read the data back as 0xFF because of TTL floating to high. I do miss the Altair and Imsai machines in a strange sort of way ;-) Clem ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh ___ Simh mailing list Simh@trailing-edge.com http://mailman.trailing-edge.com/mailman/listinfo/simh
