15 Jun
2008
15 Jun
'08
8:23 p.m.
CP-M Z80 home brew computer circuit board
bfranchuk at jetnet.ab.ca bfranchuk at jetnet.ab.ca
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20circuit%20board&In-Reply-To=5E5B27B6AB204FE39BB21B75D4C8713B%40andrewdeskt
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Sun Jun 15 12:06:33 CDT 2008
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________________________________
Andrew Lynch wrote:
-----REPLY-----
Hi! Thanks Jim for the comments. Please let me address the issues raised
by Ben:
If you look closely at the SBC design, you'll notice it has a feature even
better than a floppy controller -- it has a fully buffered IO bus! It
contains all the Z80 signals brought out to the DIN 41612 connector. The
peripheral bus adheres to the published ECB standard.
If you want floppy IO, the solution is simple -- just design one and
attach
it to the bus! I have already done this with my Disk
IO board (IDE and
NEC765 FDC) which plugs into my home brew ECB backplane along with the
SBC.
Assuming there is enough interest in these home brew
SBCs, I hope to make
a
PCB version of the Disk IO board.
Well when you get a PCB of the Disk I/O board , I'll take the set of
PCB's.
Will a 8272 (intel) Disk controler replace the NEC765? for the floppy
controler
for the track formatting for CP/M? Unicorn Electronics is my favorite
shopping for
electronic parts and I can find a 8272 there.
-----REPLY-----
Hi Ben,
Of course, the NEC 765 and Intel 8272 are virtually the same part and are as
common as dirt.
I believe Intel licensed the NEC 765A and just renamed it the i8272 or
something like that.
However, getting the FDC chip is the trivially easy part. Getting a data
separator is a much more difficult problem.
Have you tried finding an FDC9229 recently? How about a SMC FDC9216 or UMC
8326? Even the FDC1793 requires a DS chip.
I challenge you to even *FIND* a FDC9229 *datasheet* these days.
DS chips are nearly unobtainium or at least very difficult to get. I have a
few and but not many. They are hard to find.
For a DS you can probably substitute a ROM based state machine or even hack
it out using SSI TTL chips.
However, then you'll have a much larger PCB that'll cost a small fortune to
manufacture and few can afford.
If you try to use an integrated FDC with DS built in, you'll run into even
more problems.
Chips like the WD2797 and SMC9266 have built in data separators but are even
more scarce and expensive than the data separator chips.
In short, if just adding Floppy IO to a SBC were an easy task, you see more
home brew SBCs available with them.
I am trying to build an SBC that any hobbyist can afford, build reliably,
and have a reasonable chance of success.
That means compromises had to be made and some stuff had to go.
Anyone can design a great computer on paper. Making a real, tangible part
is a lot more difficult.
Using cool sounding but almost impossible to find parts seems easy but it
makes the SBC practically worthless.
If you can make a low cost Z80 SBC that includes floppy IO, I would love to
see it. I'd even buy one or two.
I look forward to seeing your design.
Thanks and have a nice day!
Andrew Lynch
15 Jun
15 Jun
9:05 p.m.
Andrew Lynch wrote:
That means compromises had to be made and some stuff
had to go.
Anyone can design a great computer on paper. Making a real, tangible part
is a lot more difficult.
Using cool sounding but almost impossible to find parts seems easy but it
makes the SBC practically worthless.
If you can make a low cost Z80 SBC that includes floppy IO, I would love to
see it. I'd even buy one or two.
But when you think about it, most early CP/M machines were
8 inch single density. Not much on a disk and that I think is
the basic format to look at. I think I seen a data separator
using a 16 bit counter at 4x? the data rate but I can't remember
where.
I look forward to seeing your design.
Thanks and have a nice day!
I can't say I am having a nice day.
I am still grumbling over not getting PAD's
PCB and LAYOUT software when I could in
the late 80's. I am looking to do a 16 bit
(2901) cpu using EEPROM (2kx8 250 ns)
and am still trying to find a schematic capture
and PCB layout program that I can afford
with through the whole parts.
Sadly all seem to be Australia. :(
Andrew Lynch
10:11 p.m.
bfranchuk at jetnet.ab.ca wrote:
Kicad for linux there are other like cadstd for winders.
Of course the last 2901 design I'd done in the early 80s was
with paper and pen! It's doable that way.
FYI using 250nS eproms will make it terminally slow unless
you do two things, use a wide microword 64bits or more and
pipeline the address and decode so you can work right to the
eprom Tacc minimum limit.
Allison
Andrew Lynch wrote:
Have you ever used 8"SSSD to do anything that required space? There isn't
enough space to run a disassembled version of the BDOS through ASM unless you
have at least two drives and don't mind doing cleanup.
Yes you can roll your own data sep it only needs three ttl packages. With all
the other hardware needed for the 765 case you end up with at least 10 chips
though If you willing to miss a few features it's been done in 7 plus the FDC
and that doesn't include the bus side of the FDC interface.
That means compromises had to be made and some
stuff had to go.
Anyone can design a great computer on paper. Making a real, tangible
part
is a lot more difficult.
Using cool sounding but almost impossible to find parts seems easy but it
makes the SBC practically worthless.
If you can make a low cost Z80 SBC that includes floppy IO, I would
love to
see it. I'd even buy one or two.
But when you think about it, most early CP/M machines were
8 inch single density. Not much on a disk and that I think is
the basic format to look at. I think I seen a data separator
using a 16 bit counter at 4x? the data rate but I can't remember
where. I look forward
to seeing your design.
Thanks and have a nice day!
I can't say I am having a nice day.
I am still grumbling over not getting PAD's
PCB and LAYOUT software when I could in
the late 80's. I am looking to do a 16 bit
(2901) cpu using EEPROM (2kx8 250 ns)
and am still trying to find a schematic capture
and PCB layout program that I can afford
with through the whole parts.
Sadly all seem to be Australia. :(
Andrew Lynch
17 Jun
17 Jun
12:09 p.m.
Allison wrote:
Have you ever used 8"SSSD to do anything that required space? There
isn't
enough space to run a disassembled version of the BDOS through ASM
unless you have at least two drives and don't mind doing cleanup.
I never could run the CP/M system I was using for more than 30 minutes
with out
the floppy stepper sticking. That was fun working with it. Still how do
you transfer
stuff from a floppy ( or file online ) to a CP/M system with no
external I/O devices?
Yes you can roll your own data sep it only needs three
ttl packages.
With all the other hardware needed for the 765 case you end up with at
least 10 chips
though If you willing to miss a few features it's been done in 7 plus
the FDC
and that doesn't include the bus side of the FDC interface.
That I would like to see.
Kicad for linux there are other like cadstd for winders.
Of course the last 2901 design I'd done in the early 80s was
with paper and pen! It's doable that way.
I still am using paper & pen.
Mind you I have to buy JAPANESE pens
since the quality of the USA stuff is all cheap Chinese imports.
Now that I have a serious cad program - DIPTRACE on order
I think I will put the design in hardware.
FYI using 250nS eproms will make it terminally slow
unless
you do two things, use a wide microword 64bits or more and
pipeline the address and decode so you can work right to the
eprom Tacc minimum limit.
I got that covered if I read the 2901 data sheets
correctly.
I will be using a 6809 style memory cycle optimized for
D-RAM access and clock the 2901 in 4th phase of
the memory cycle. This is retro computing project for the feel
of the late 1970's not using a 8 bit CPU. I am aming for
a 800ns memory cycle and the slow access of micro-code
is not a problem. The only thing pipelined is the next memory
cycle - Read/Write/Refesh and the default is refresh while
doing the the 1st cycle of op-code decoding. The front
panel does RUN/STOP, Single Instruction,Address Load,
Deposit,Read.
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3 comments
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participants (3)
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ajp166＠bellatlantic.net -
bfranchuk＠jetnet.ab.ca -
lynchaj＠yahoo.com