Just looking at some 6502 stuff, and the program counter notes at
http://www.6502.org/tutorials/6502opcodes.html#PC say:
"When the 6502 is ready for the next instruction it increments the program
counter before fetching the instruction."
... which seems to imply that T-cycle 0 of an instruction first increments
PC, then fetches the opcode from the memory location pointed to by PC.
Which seems nuts, as it would also mean that either jump addresses would
have to be off by 1, or at the start of T0 the CPU would have to determine
what the _previous_ instruction was and then either increment PC or leave
it alone accordingly. And all of this would have to happen before the
address is placed on the address bus approximately 1/4 of the way into T0.
I expect that what actually happens is that PC's contents are latched onto
the address bus during the clock-low half of T0, R/W is asserted, and
*then* PC is incremented. During the subsequent clock-high half of T0, the
data bus will reflect the contents of [PC] as it was at the start of T0,
and the PC increment will complete, so that at the end of T0 PC is pointing
to either an operand byte for the current instruction, or the next
instruction in the sequence (if the current instruction has no operands).
Can anyone confirm? Although technically I suppose the text on the site
would still be accurate, because the increment would actually have begun
before the fetch had entirely completed, but the way it reads to me is that
the opcode fetch happens at [PC+1], not [PC]...
The text then goes on to say: "Once it has the op code, it increments the
program counter by the length of the operand, if any."
6502 operands can be 1 or 2 bytes in length; the above seems to imply that
for a 2-byte operand it would add 2 to PC - meaning it would have to fetch
the first operand byte from PC-1 (and there's no PC-decrement logic in
sight). I expect that what it really does is fetch the first byte from PC
(which will have been incremented during the opcode fetch cycle),
increments PC by 1, fetches the second byte, and increments PC again.
Right? :-)
Now, someone on the BBC micro list said they think that the 6502 might
always do an operand byte fetch immediately after an opcode fetch, even if
that instruction doesn't have any operand data - simply because it takes
time for the CPU to decode the instruction. If it turns out that the
instruction doesn't have an operand, it avoids doing the PC increment that
would have been done if an operand were present (which means that at the
next cycle, which the CPU will perform as an opcode fetch, the same byte is
re-read from memory and interpreted as an instruction).
Does anyone know if this "always read" is what happens? Or is the
instruction decoding actually quick enough for the CPU to know by the end
of T0 that there's no opcode data (and so it can reset its cycle counter
and perform the next cycle as an opcode fetch)?
cheers
Jules
I have come a across someone selling two different KFQSA boards. Is there a
significant difference between a KFQSA-SG-RE and a KFQSA-SF-RE?
Regards
Rob
Hi everybody!
More shameless classic parts trafficking. These go live on 11/12/ @ 2pm on
epay
251183147655 DEC 11/04, dual sms floppy drives, Vt100 and rt-11
251183206220 DEC tm03 controller unit
I'll be putting some apollo stuff up and maybe some other stuff later this
week. Of course, mention your a member of the ccmp list and get some
freebies thrown in.
Cheers
tom
Some of you may know of this item already but some may not, and might be
interested. It's a short 10min YouTube video on one of the units in my
collection: An OS Challenger 1P
http://youtu.be/zrOYkKf5Y5k
Terry Stewart (Tez)
Rik,
I have an HP382 that I would like to resurrect. It has no SCSI drive
in it, so if you still have ISO for HP-UX 9.10 available ( is it two
CD's ?) , I can get the machine back into service.
Regards,
Hutch
>* -----Oorspronkelijk bericht-----
*>* Van: cctech-bounces at classiccmp.org
<http://www.classiccmp.org/mailman/listinfo/cctech>
[mailto:cctech-bounces at classiccmp.org
<http://www.classiccmp.org/mailman/listinfo/cctech>]
*>* Namens mls
*>* Verzonden: donderdag 10 november 2011 6:30
*>* Aan: cctech at classiccmp.org
<http://www.classiccmp.org/mailman/listinfo/cctech>
*>* Onderwerp: Re: ISO HP-UX 9.10 install CD
*>*
*>* Rik,
*>*
*>* Back in 2009, you had posted on this thread that you could make HP-UX 9.10
*(HP
>* 9000 series 300) ISO's available, but the thread, basically ended there.
*I have
>* been looking on and off for this software for some time for an HP 360 that
*I
>* have.
*>*
*>* Thanks,
*>* Chris
*
Chris,
I uploaded the iso's to several members of this list, if you have a ftp
server you can have it.
And maybe you don't know bout on the HP-museum site :
http://hpmuseum.net/exhibit.php?swc=6
you can download a lot of software for the HP 9000/300 series
-Rik
Let's try this again...
Can I get a step-by-step on going from a fresh install of System 6 on a
Macintosh SE/30 to being able to share files from a netatalk server?
Here's what I have in inventory:
System 6 install floppies
Asante PSD ethernet board for SE/30 with install floppy
MacTCP 2.0.6
MacTCP 2.1
MacTCP Ping 2.0.2 (doesn't recognize MacTCP 2.1)
ZM Appleshare Workstation 3.5
Network Software Install 1.5.1
The ethernet board blinks when plugged into a network. That's as far as I
can get. The interface for MacTCP is impenetrable.
--
David Griffith
dgriffi at cs.csubak.edu
A: Because it fouls the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?
I need an HP 21MX/E FAB board, preferrably with E-FPP and E-DMI. If
possible, would also like a blank FAB as a spare. Even if all you have
is a blank board, I'd still be interested and I'd just burn the roms
for it.
Anyone have any of the above and willing to make some trade or $$? If
so, drop me an email!
J
Anyone here familiar with the Progress database and 4GL? I have a pretty complete set of manuals and a partial set for v8 that I'd be willing to give for free minus postage... Anyone interested?
-Ben
Hi
I've updated the N8VEM wiki PCB inventory list to correct several
inaccuracies and correct quantities available.
There are many PCBs remaining so if you are looking for some please contact
me.
Especially there are some recent PCBs for the ECB like the DSKY, Color VDU,
MF/PIC, and DiskIO V3 which may be of interest to you.
There are technical data for these PCBs on the N8VEM wiki including
schematics, PCB layout, KiCAD EDA files, software, photos, etc.
http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder¶m=Board%20Informa
tion
Using the N8VEM mini SBC V8 and/or the ECB backplane PCBs is sufficient to
build your own system.
There are sufficient 6x0x PCBs to build 6502, 6809, or 6802 CPU based
computers.
There are some mini-boards like AT2XTKBD for $5 each that allow connecting
AT/PS/2 keyboards to PC/XT computers.
Also there are ECB to Z80 socket adapters which allow the ECB boards to be
connected to a Z80 socketed CPU rather than an ECB bus.
Here is the link for your review:
http://n8vem-sbc.pbworks.com/w/page/35044530/PCB%20Inventory
The PCBs are $20 each plus $3 shipping in the US and $6 elsewhere.
If you are considering getting one or more now is the time!
I am stuck and need to move the remaining boards to free up the funds to do
other board orders/reorders.
I appreciate all the community support for the N8VEM home brew computing
project. Thanks and have a nice day!
Andrew Lynch
PS, there is also one S-100 8088 CPU board PCB remaining.
