---- The Poqet PC --------------------------------------------------------------
 Home  FAQ  LIST  SOFTWARE  DOCUMENTATION  MUSEUM  LINKS

Poqet PC Mailing List Digest
Volume 002, Number 009, 4 Sep 1997

Table of Contents


 <
Previous (Vol. 002, No. 008)

UP (to archive list)
 >
Next (Vol. 002, No. 010)

  1. Re: Digest poqetpc.v002.n007 by Sabrodsky@xxxxxxxx
  2. Looking for... by jdmorgan@xxxxxxxx (Justin D Morgan)
  3. Re: Digest poqetpc.v002.n007 by sharriso <sharriso@xxxxxxxx>
  4. PCMCIA Discussion (was "Re: Digest poqetpc.v002.n006") by Bryan Mason <bmason@xxxxxxxx>

Digest Articles

Re: Digest poqetpc.v002.n007 by Sabrodsky@xxxxxxxx


From: Sabrodsky@xxxxxxxx
Subject: Re: Digest poqetpc.v002.n007
Date: Wed, 3 Sep 1997 16:34:01 -0400 (EDT)

Hi:
When I had my Poqet I used to save files in text and then pop the card in my
Omnibook 300 and read them with no problem.
Regards
By the way, anyone have a Poqet they are selling cheap?


Looking for... by jdmorgan@xxxxxxxx (Justin D Morgan)


From: jdmorgan@xxxxxxxx (Justin D Morgan)
Subject: Looking for...
Date: Wed, 3 Sep 1997 18:20:49 -0400

I'm looking for a used Poqet PC. Know where I can get one? It would be
nice to have a new one, but I can't afford that.

That is, if I don't win one in an auction. I placed a bid on one for $45,
and that includes shipping. It also has the serial cable, PC transfer
software, and a memory card. Is that a good price or not?

Is there any place where you can still buy software for the 8088?
----------------------------------------
Sent by Justin Morgan
jdmorgan@xxxxxxxx
Practice makes better.
----------------------------------------


Re: Digest poqetpc.v002.n007 by sharriso <sharriso@xxxxxxxx>


From: sharriso <sharriso@xxxxxxxx>
Subject: Re: Digest poqetpc.v002.n007
Date: Wed, 03 Sep 1997 19:49:13 -0500
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
References: <199709030210.TAA09813@xxxxxxxx>

I have transferred files using both the serial null modem and via a
pcmcia slot on a laptop I use at work.  The latter is vastly more
convenient.  I understand it is advisable to format the memory card
using the Poqet, or it may not be recognized by the Poqet if formatted
elsewhere.

Steve Harrison

Ernest J. Yanarella wrote:
> 
>      Has anyone had experience using the PCMCIA slot on their laptop to
> transfer and convert files to its floppy disk.  Mike Fetterman's recent
> e-mail query elicited this question.  I find the present file transfer from
> Poqet to Desktop PC so cumbersome and confusing that I have let me teenage
> son do it.  Now that he started his first year of college, I am left high
> and dry.  I like the Poqet for its convenience, small size, and
> portability, but whenever I get a long file on it, I dread the prospects of
> switching it to the desktop and to Word.  Help!


PCMCIA Discussion (was "Re: Digest poqetpc.v002.n006") by Bryan Mason <bmason@xxxxxxxx>


From: Bryan Mason <bmason@xxxxxxxx>
Subject: PCMCIA Discussion (was "Re: Digest poqetpc.v002.n006")
Date: Wed, 03 Sep 1997 23:38:31 -0700
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"

At 09:07 PM 8-30-97 -0400, Michael Fetterman wrote:

[...]

>Also, I know it is in the FAQ from Bryan, but could some knowledgeable 
>person here initiate a discussion of the type and limitations of PCMCIA 
>RAM cards (re: voltage, FRAM vs SRAM, linear, etc) as used in the Poqet ?


Well, here's what I know about PCMCIA.  I hope it helps beyond what's in
the FAQ.

Everyone please add what you know, clarify what might be a little
confusing, correct me where I'm wrong, or pose questions to the rest of the
group. 

SRAM CARDS
----------
"SRAM" = "Static Random Access Memory"  SRAM is memory just like any other.
 With static RAM, the memory does not have to be refreshed on a regular
basis.  This is different than the kind of memory in your desktop computer,
which is DRAM (Dynamic Random Access Memory).  In order for DRAM to hold
its contents, it has to be actively refreshed from time to time.  Because
SRAM doesn't require refreshing, it makes an ideal memory technology for
portable PCMCIA cards -- you just have to provide a power source and the
memory will keep its data as long as there is power.  SRAM is also good for
PCMCIA cards because it is relatively low power and has very fast access
times (relative to DRAM).

The bad thing about SRAM is that it is fairly expensive (relative to DRAM
and Flash) and you can't pack as much capacity into a SRAM chip as you can
with DRAM and Flash.  A single SRAM memory bit requires four transistors,
whereas DRAM and Flash only require one transistor per bit (not including
the addressing circuitry).

SRAM VOLTAGES
-------------
To read and write most SRAM, you need a 5 volt power supply.  If all you
want to do is retain the data, but not access it, then all you need is 3
volts.  All PCMCIA SRAM cards have a small 3 volt battery built in to them
so that they will retain their data when they are not connected to a host
computer.

The electronics inside the Poqet PC are designed to run at both 3 and 5
volts.  The way the Poqet PC's circuitry works is that the system will run
at 3 volts and a lower clock speed when it's not really doing anything, and
then it will switch to 5 volts and a higher clock speed when it really
needs to do some data crunching.

Before it tries to access an SRAM card, the Poqet PC switches to 5 volts,
waits for the power supply to stabilize, and then begins reading from or
writing data to the card.  The only problem is that, as the Poqet's AA
batteries begin to die, it can't maintain that 5 volt level any more.  The
system voltage begins to drop closer to 3 volts.  So with old batteries,
the SRAM card is being accessed with a 3 volt power supply.  If the card
isn't designed to support read/write accesses at 3 volts, then you'll get
read errors or write errors -- data corruption and loss.  That's why the
Poqet requires a "3 volt" SRAM card.  Unfortunately, the Poqet is nearly
(if not completely) alone in this requirement, which is why it's so hard to
find 3 volt SRAM cards.

FLASH Memory
------------
Flash Memory (also called Flash RAM or Flash ROM) was invented by Intel.
Flash Memory is a type of EEPROM (Electrically Erasable Programmable
Read-Only Memory).  Flash Memory is like a ROM (Read-Only Memory) because a
Flash Memory chip will store data even when power is removed from the chip.
 But unlike ROM chips, you can also erase and reprogram the memory chip.  

Flash is much cheaper than SRAM (used to be about half the price, I don't
know what it is today).  The limitation of flash is that you can't erase
individual bytes -- you have to erase an entire block (like 512 bytes - 512
KB).  So to change a single character in a file that's stored in a Flash
Memory chip, you might have to erase and rewrite the whole file.  There are
ways around this, however.

"Linear" Flash
--------------
The first kind of PCMCIA Flash cards were "Linear" Flash (I'm not 100% sure
if that's what everybody called them, but that's the way we referred to
them at Poqet).  Linear Flash cards were just a bunch of Flash Memory
inside a flash card.  To put files on the card, you had to program the card
all at once.  We used to use an old Databook PCMCIA card reader/programmer
and a program that Databook wrote called "TCXCOPY" to program the cards.
TCXCOPY did some magic where you could always add new files to a card, but
if you wanted to remove files, you had to erase the whole card and start
over.  

That's the way it worked on the Poqet.  You used TCXCOPY to add files to
the card, and when it got full, you used TCERASE to erase the card and
start over.  Not a great solution, but it worked pretty well when you could
get 4 MB of Flash storage for the price of 2 MB of SRAM storage.

The other way you could use Linear Flash was to use a "Flash File System"
(FFS).  The Flash File System drivers would run in DOS and would
automatically manage the Flash card for you.  So if you wanted to replace a
file, the Flash File System would automatically erase and rewrite the file
for you.  With FFS, you didn't have to worry about the TCXCOPY/TCERASE
thing.  

Alas, we never got a Flash File System working on the Poqet.  Actually, FFS
didn't seem to be around very long because something much better came along
-- SunDisk cards.

SunDisk
-------
SunDisk had a really cool idea.  They decided that the Flash memory
technology was great, but that the hassle of managing the memory with
TCXCOPY/TCERASE and/or FFS was a major pain.  So what they did was to take
a bunch of Flash Memory and put it in a card with a microcontroller that
had the task of managing the memory.  On the other side of the
microcontroller was the newly standardized PCMCIA/ATA interface.
PCMCIA/ATA is a standard that makes it so a PCMCIA card looks alot like the
standard ATA disk interface that's in most PCs.

Anyway, the block diagram of a SunDisk card kindof looks like:

HOST COMPUTER <==============> MCU <====> FLASH MEMORY
               (PCMCIA/ATA)

A SunDisk card is, in concept at least, identical to a hard disk drive.
The host computer talks to a microcontroller which is responsible for
managing a bunch of memory.  In a disk drive, the "bunch of memory" is
located on rotating platters.  In a SunDisk card, the "bunch of memory" is
actually a couple megabytes of Flash Memory.  The host computer just says
"write this data to location such-and-such" and the microcontroller is
responsible for doing all of the "program/erase/reprogram" stuff that we
used to do with TCXCOPY/TCERASE.

Pretty cool (at least I think so).

Several years ago, SunDisk changed their name to "SanDisk."  The rumor was
that Sun Microsystems felt that SunDisk was infringing on their copyrights.
 I don't know if that's true, but that was the rumor.

The only problems with SunDisk cards are:
1) The amount of time required to write data is pretty slow.  Faster than a 
   hard drive, but slower than an SRAM card.  This because of the whole 
   program/erase/reprogram cycle that needs to be done -- the erase/reprogram 
   cycle takes a relatively long period of time.
2) They don't work on Poqet PCs.
   (Well, some actually work on Poqet PC Plus's -- but not on Poqet PC 
   Classic's or Prime's.)


______________________________________________________________________
Bryan Mason, Menlo Park, California, USA, Earth
e-mail:                <bmason@xxxxxxxx>
Poqet PC Home Page:    <http://www.best.com/~bmason/PoqetPC/>
Poqet PC Mailing List: <PoqetPC@xxxxxxxx>



Filename: PoqetPC/mailing-list/cgi/show-digest.htmt
Date Created: 30 Nov 1996, Last Modified: 13 May 2009
Created by Bryan Mason - E-Mail: poqetpc<at>bmason<dot>com