>From: "Michael B. Brutman" <mbbrutman at brutman.com>
>
>
>I don't think that the lack of a DMA controller on the PCjr really
>slowed it down any. The old double density drives have a data rate of
>250,000 bps. If the data is presented one byte at a time, that is just
>31250 bytes per second. Even with multiple I/O clock cycles per byte to
>get it to the processor and then to memory, a 4.77Mhz processor can keep
>up with that easily.
>
>Where the lack of DMA would hurt you is on a much faster interface, such
>as a hard disk. Then you wouldn't have any cycles to spare, the the
>difference would show up.
Hi
I don't think the early PC's used DMA for the hard disk.
The HD controllers usually had sector or track buffers.
The program would wait until the buffer was full and
then just move it by software to memory. The floppies
needed DMA because the controllers didn't buffer more
than one byte. The processor would have had to dedicate
it self to the one task without interrupts.
Dwight
I saw an auction which reminded me of the days when the PC and XT
came out, but before clones or otherwise appeared, and before such
as AST were dominating the market.
This auction is for a "zukerboard" 576K mem expansion. 6801436037.
I remember the hype for zucker that they were going to wreck the
market.
The only reason this has any significance is that I believe this was one
of the
AST wannabe's, or even was larger than AST, pre the days when they
started making systems.
I know of at least Zucker, Tecmar (marty tech, I don't remember marty's
last name, but he was some sort of PHD ohio type, I think).
A number of companies were based here in Orange County, California,
and provided a lot of cheap stuff as they cratered, and the local
scrappers
got their. stuff and sold it off.
Processor Technology (? I think) went big time and cratered.
I remember a little shop here in Santa Ana which had the first clone of
the IBM PC. It was a single board which had 640k memory, allowed
using 64k memories, instead of the 16K memory that the PC and XT
earlier models used.
It was called "Superboard" and was no relation to Supermicro, which
came much later. It had a bios that usually worked, but also had,
conveniently, a spot for up to 6 eprom chips, so you could put in a
PC bios if you could get a copy.
The PC used either EProms, (16K I think) and the Roms that were
shipped with the BIOS were registered. The standard Data I/O would
not read them since they were not programmable, and needed their
output enabled to read the data.
But once someone had them in the 2716's, it was easy to get them
running in your superboard.
First systems had a 63 watt P/S, and IBM cards if you could find
them for video. Also there was no floppy controller on the first
board.
Maybe others of you can recall expansion card makers, of such
things as serial, parallel, memory, floppy, then hard drive, etc.
Jim
I just examined a "Zilog Z80 Microcomputer System", Model 05-6002-05 (MCZ 1/80
60K), Serial Number 744 and an associated terminal, Dentronix Systems SCS200,
Serial Number 395. The Z80 development system looks in good shape (but needs
exterior cleaning). It has two built-in 8" FDD and it has both a terminal
port and a serial or parallel port. The matching Dentronix terminal is so
clean, it looks brand new.
The system comes with a complete set of manuals, which includes schematics of
the "mainframe" and plug-in boards. Unfortunately, there is no software
available.
The system and terminal are located in Mountain View, California and I'm
guessing a total weight of 50 lbs.
If this is of interest to you, make an offer for it directly to me - and I'll
pass that information on to it's owner.
If there are no takers, I'll likely buy it myself to keep it from going to a
scrapper (in about a week).
Cheers,
Lyle
--
Lyle Bickley
Bickley Consulting West Inc.
Mountain View, CA
http://bickleywest.com
"Black holes are where God is dividing by zero"
>Date: Thu, 29 Sep 2005 11:55:18 -0700
>From: Eric J Korpela <korpela at ssl.berkeley.edu>
>Subject: Re: Tristate Buffer Output if Input is High-Z?
>Anyone have a datasheet for Hitachi HM511000AJP8 DRAMs? It's used in at
>least some IIfx SIMMS.
>
>What's the deal with parity on the IIfx? Is the parity bit stored off the
>SIMM? The technote
>http://developer.apple.com/technotes/hw/pdf/hw_25.pdfmentions parity,
>are there 9-chip SIMMS on the IIfx? Or is the parity stored
>on a separate RAM on the mainboard? Since your max memory is 8x(4Mx8bit bit
>SIMMS) accessed 32 bits at a time (I assume) you'd only need 1 Mbit of
>parity RAM if you do parity across 32 bits.
You are unlikely to ever see a IIfx that actually implements parity.
It was an option for the IIfx but was very rare in practice. In
virtually all cases the IIfx uses an 8 bit 64 pin SIMM with no
parity. The presence of parity on the SIMM will not affect
operation, because on a non-parity IIfx, the SIMM pins for parity
connections are NC.
A IIfx SIMM built for parity will have 1/8 more capacity. The extra
storage for parity is on each individual SIMM. The pinout for the
SIMMs is in "The Guide to the Macintosh Family Hardware". It's one
of those Addison Wesley books.
I don't have that particular datasheet on hand. But if you get one,
I'd like a copy as well. I imagine it's a pretty standard 1M X 1
DRAM chip.
>Date: Thu, 29 Sep 2005 14:01:37 -0700
>From: Eric J Korpela <korpela at ssl.berkeley.edu>
>I also notice that the table on page 2 of the technote contradicts the IIfx
>section. The table says you can put up to 128MB in a IIfx, but the IIfx
>section says the biggest SIMM allowed is 256kx8.
I think you misread that somehow. The tech note states that the IIfx
does not support 256KB SIMMs. It gives examples of memory
configurations up to 32 MB, using 4 MB SIMMs, although there's a
consistent typo in the example where megabit is written instead of
megabyte.
But the maximum memory capacity is 128 MB, using eight 16 MB SIMMs.
That was/is the maximum capacity for most of the Mac II family. The
exceptions are the original Mac II (68020 based), the Mac IIsi
(supports 16 MB SIMMs, but only has 4 slots) and the abomination with
variations known as the IIvi and IIvx.
As far as I know, there can't be 30 pin SIMMs with capacities larger
than 16 MB, because there are only 12 address pins available and 12 X
2 = 24 and 24 address bits yields 16M addresses. There aren't any NC
pins left to convert to additional address lines, unless one steals
the parity pins.
Jeff Walther
I recently acquired through the generous efforts of a member here, a
Commodore PET 2001-32B. It boots up to just garbage characters on the
screen. Any quick things I can check or a 'suspect' part? Also if anyone
knows where I can obtain a schematic for this beauty, please let me know!
Thanks
>From: "Hans Franke" <Hans.Franke at siemens.com>
>
>Am 29 Sep 2005 14:41 meinte Star Master:
>
>> I recently acquired through the generous efforts of a member here, a
>> Commodore PET 2001-32B. It boots up to just garbage characters on the
>> screen. Any quick things I can check or a 'suspect' part?
>
>It's a PET, so first thing is just to press back all chips
>firm into their sockets. Solves 98% of all Commodore problems.
>
>Gruss
>H.
>
Hi
I'll make my standard comment here. Putting
DC#4 or similar materials onto pins before
putting things back together will make a difference.
This is especially true for the power pins that
would otherwise tend to over heat because of
contact resistance.
Dwight
Hi
I believe there are 4 holes that you can see in the bottom
plate that go to empty threaded holes in the frame of the printer.
You need to put these screws in and it will clamp the
printer unit to the frame so it doesn't wobble around
on the rubber mounts.
I'd tell you what thread but my unit came without them :(
Dwight
>From: "Vintage Computer Festival" <vcf at siconic.com>
>
>
>Grrr, I hate bringing up old topics, but I can't find anything in the
>archives or on Googl.e
>
>I'll be shipping an ASR32 and want to lock the typing unit. I've seen a
>message from Tony mentioning a "transit screw" that secures the typing
>unit to the base.
>
>Can anyone elaborate?
>
>--
>
>Sellam Ismail Vintage Computer Festival
>------------------------------------------------------------------------------
>International Man of Intrigue and Danger http://www.vintage.org
>
>[ Old computing resources for business || Buy/Sell/Trade Vintage Computers ]
>[ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]
>
>
>From: "Ashley Carder" <wacarder at earthlink.net>
---snip---
> but I can't get the keyboard to type in local mode. The keys don't press down
all the way.
Hi
As another mentioned, it most likely has a keyboard
reset problem. If it still has the H shaped coupling
between the keyboard and the printer, remove this
and see if you can reset the keyboard by actuating
the crank manually. Also, look to see if the printer
assembly is actuating the reset by manually turning
the motor and watching where the H coupling goes.
This is driven by ( as I recall ) a clutch near the
distributor.
Dwight
Just noticed your file on google. Are you still in need of paper tape or more to the point for me , do you still have fan-fold paper tape to get rid of?
Ray Plett at mts.net
>Date: Thu, 29 Sep 2005 17:51:13 -0400
>From: Paul Koning <pkoning at equallogic.com>
>Subject: Re: Tristate Buffer Output if Input is High-Z?
> Tony> An analogue switch IC is a similar device, and those do
> Tony> exist. The problem is finding one that will switch quickly
> Tony> enough (I would guess in a few nanoseconds) for this
> Tony> application.
>
>No problem.
>
>Quickswitches are rated to several hundred Megahertz. If that isn't
>good enough, you can use microwave switch transistors. I don't know
>the max switch rate of either, but presumably any transistor capable
>of carrying microwave frequencies can switch on/off in a nanosecond or
>better.
>Date: Thu, 29 Sep 2005 15:16:46 -0700 (PDT)
>From: "Dwight K. Elvey" <dwight.elvey at amd.com>
>Subject: Re: Tristate Buffer Output if Input is High-Z?
>>No problem.
> The problem is as Tony mentioned, you get no buffering.
>This means you can't expect to put the mux too far from
>the inputs on either side. You are really better off
>using something like '245's.
Thank you, gentlemen, and that includes the respondents I did not
quote above (previous digest). I really appreciate all the great
information and leads.
I started with Pericom (as one person suggested) as I am familiar
with some of their products and worked backwards from there. It
appears that they are calling the product which I want "Bus Switch".
Once I knew that, there's a nice selection available on Digi-Key,
although I'll check Mouser later for better pricing.
The selection is not quite as nice as I'd like, because there's
nothing analogous to the SN74ABT241A. The nice thing about the 241
is that it divides its eight buffers into two groups of four with
independent enables for the two groups of four. Okay, that's like a
244. However, the 241 has one active high enable, and one active low
enable, while both enables on the 244 are active low.
So I'll need an inverter in line with one of the OE pins on the bus
switches, which isn't the end of the world, but its not as elegant as
the SN74ABT241A would have been. The candidates are the Pericom
PI5C3244 or the TI SN74CBT3244.
The speeds on these components look fast enough, the time to switch
>from high-Z to conducting has a maximum value of about 6 ns on the
Pericom and 8 ns on the TI. I'm not certain they used the same test
conditions. Minimum times are 1 ns. Both have a propagation time of
.25 ns from A to B or B to A once the switch is enabled.
Dwight, can you elaborate on why I'd be better off with something
like '245s? I either don't understand your point, or I have not
explained my intent clearly enough. I am trying to emulate the SIMM
on a IIfx. The only difficulty is getting X 4 DRAM chips to look as
if they have separate D and Q pins.
On stock IIfx SIMMs, the data signals are not buffered on the SIMM,
they come directly from the DRAM chip to the SIMM connector. On my
SIMM, they will go from the DRAM chip, through a bus switch (or
tristate buffer) and then to the SIMM connector. So, unless too much
signal strength is lost going through the bus switch, I do not
understand why I'd need a buffer there to strengthen or clean up the
signal. Or are you saying that I should have a latch there to hold
the signal for some time after my switch control signal goes inactive
to make sure that hold times are supported?
The pinout on the SN74ABT241A (buffer) and the SN74CBT3244 (switch)
are the same (the PI5C3244 is also the same but comes in a smaller
package) and the same packages are available. I jumped the gun and
already have some SN74ABT241A on hand.
So I think what I'll do is design my first set of SIMMs with the
posibility of taking the OE signal for the Data Out side of the
buffer/switch either directly from WE, from WE run through an
inverter (WE'), or from WE AND CAS'. The inverters and AND gates
are available in tiny SC70 packages (similar to SOT23).
Then I can test the Buffer with WE (OE is active high) as control for
Din and Dout. The Buffer with WE AND CAS' (OE is active high) as
control for Dout. And the Bus Switch with WE' (OE is active low) as
control for Dout.
Jeff Walther
