From: darrylo@hpnmdla.sr.hp.com (Darryl Okahata)
Subject: Re: Smith Corona 32K cards

[ Take note that, while I am an HP employee, I have nothing to do with
  the division that makes calculators.  ]

In comp.sys.handhelds, blair@en.ecn.purdue.edu (Marc E Blair) writes:

> I got my calculator back from hp a couple days ago, and boy did I feel
> dumb when I read the note they put in. "Dead Batteries - replaced.
> Machine meets all specs" OK, I should have checked the batteries.. but
> the batteries were less than a month old, and I just ASSUMED that they
> would still be functional. And usually, the HP48 gives me a warning
> that the batteries are about to die leaving me a few days to change
> them. But there was no warning. I think I read on the net that if the
> pins on the SMC cards did not get pulled up to a sufficient voltage
> the card would lock and batteries would drain.

     ... and you could seriously damage your calculator.  (No, I'm not
kidding.) 

     At the end, I've included some old messages that describe why.  You
can decide if you want to play russian roulette with your HP 48SX (I
certainly don't).

     -- Darryl Okahata
	Internet: darrylo@sr.hp.com

DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion or policy of Hewlett-Packard or of the
little green men that have been following him all day.
===============================================================================
  From steveh@hpcvra.CV.HP.COM Fri Mar	1 17:00:00 1991
  From: steveh@hpcvra.CV.HP.COM (Steve Harper)
  Date: Thu, 10 May 1990 22:46:09 GMT
  Subject: RE: HP48SX Memory Card Pricing
  Organization: Hewlett-Packard Co., Corvallis, OR, USA

  There has been a substantial	amount	of  comment  regarding	the
  memory cards for the HP48SX and their prices.	 My purpose in this
  response is not to attempt to justify any particular	price,	but
  rather   to	present	 the  technical	 reasons  why  there  is  a
  substantial price difference between the memory cards	 and  other
  types of expansion memory for PC's, for example, with which users
  are probably more familiar.
  
  Some users have correctly pointed out	 that  the  memory  in	the
  cards	 is  static  RAM  rather  than dynamic RAM commonly used in
  PC's.	 Dynamic RAM uses one transistor and a capacitor  for  each
  bit of memory whereas static RAM requires either four transistors
  and two resistors, or six transistors.  The net result is that an
  equivalent amount of static RAM is much larger and therefore much
  more expensive than dynamic RAM.  The advantage  is  that  static
  RAM  doesn't	need  to continually be running and drawing current
  (refresh cycles) to retain the contents of memory.
  
  In addition, the static memory used in the cards is not just	any
  static  memory,  but	is  specially processed and/or selected for
  very low standby current.  This allows the backup battery in	the
  card	to  keep  memory  alive	 for  a very long time, rather than
  requiring the user to replace it every few months.   The  special
  processing  and/or  special  testing	to select low current parts
  adds to the already higher cost of the static RAM chips.
  
  The standard molded plastic DIP package used for most	 integrated
  circuits,  including	memory	chips,	is  relatively	inexpensive
  because of its simplicity and the huge  volumes.   Unfortunately,
  these	 packages  are	too  large  to	put  into  a  memory  card.
  Therefore, the card manufacturer mounts  the	individual  silicon
  memory  chips	 directly  on a special thin PC board together with
  the memory support  chips.   Because	multiple  chips	 are  being
  placed  in a single hybrid package in a special process which has
  lower volume, yields are lower and this again causes the cost	 to
  be  higher.  Indeed, the yield becomes exponentially worse as the
  number  of  chips  and  interconnections  increases  in  such	  a
  packaging process.
  
  In addition to the memory chips themselves, two  more	 integrated
  circuits  and	 several discrete components are required for power
  and logic control.  A bipolar technology chip senses the external
  voltage  and	switches  the  power to the chips from the internal
  keep-alive battery as needed.	 A CMOS gate  array  chip  protects
  the memory address and data lines from glitches/ESD when the card
  is not plugged in.  This chip also generates the proper  enabling
  signals  when	 there are multiple memory chips in the card, as is
  presently the case with the 128 Kbyte RAM card.  These chips must
  be  designed	for extremely low current, just as the memory chips
  are.
  
  In addition to the battery and  the  battery	holder,	 the  other
  mechanical  parts  are  important, too.  The molded plastic frame
  holds the PC board and provides  the	foundation  for	 the  metal
  overlays  and the shutter-and-springs assembly which protects the
  contacts from	 ESD  and  from	 contaminants.	 The  write-protect
  switch  is  also an important feature.  It is quite expensive for
  the manufacturer to make the tools necessary to fabricate each of
  these	 parts	as  well  as  the  tools  to  assemble and test the
  complete card.  While the volume of memory  cards  is	 relatively
  low  this  tooling cost represents a significant part of the cost
  of each card.
  
  Admittedly, there are other alternatives, such as those presently
  used	in  PC's,  to  provide	a  memory expansion capability.	 To
  provide that kind of expansion would require the calculator to be
  much	larger	than  it  is  and possibly more expensive.  This is
  clearly very undesirable.
  
  Other features that were felt to be essential were the ability to
  distribute  software applications and to share and archive/backup
  user-created programs and data.  Other expansion alternatives	 do
  not provide these important benefits.	 The IO capabilities of the
  calculator provide these features only to a limited degree.
  
  One other item bears repeating here: Memory cards for use in	the
  calculator  will  clearly indicate that they are for use with the
  HP48SX.   Other  memory  cards  exist	 which	 are   mechanically
  compatible  with the HP48S, but these cards cannot be relied upon
  to work electrically in the calculator.   The	 HP48SX	 cards	are
  designed  for	 a  lower  supply  voltage range.  Use of the other
  cards may cause memory loss, and under certain circumstances	may
  even damage your calculator electrically.
  
  From steveh@hpcvra.CV.HP.COM Fri Mar	1 17:00:00 1991
  From: steveh@hpcvra.CV.HP.COM (Steve Harper)
  Date: Fri, 11 May 1990 16:52:07 GMT
  Subject: Re: Memory Card: Give Us *True* Facts!
  Organization: Hewlett-Packard Co., Corvallis, OR, USA
  
  My previous statement that under certain circumstances the
  calculator may even be damaged electrically is not a ploy.
  If the calculator's internal power supply voltage happens to
  be near the low end of the range, say 4.1 V, and the voltage
  at which the card's voltage control chip shuts it down
  happens to be near the high end of its range, say 4.2 V (this
  can and does occasionally occur for the non-HP48SX cards),
  then the calculator will start to drive the memory address
  lines and the card will still have these clamped to ground
  (that's what it does to protect itself when there is not
  sufficient system voltage to run).  This unfortunate situation
  may simply trash your memory, or if the calculator tries
  to drive enough of the lines high at the same time, several
  hundred milliamps may flow...for awhile that is, until something
  gives up...  On the other hand, your calculator and a particular
  non-HP48SX card may work just fine if those voltages happen
  to be at the other end of their ranges.  These voltages are
  also slightly temperature sensitive.	It may work in the
  classroom or office and not at the beach, or vice versa.
  The voltage trip point of the HP48SX cards has been set
  lower (a different voltage control chip) so that this cannot
  occur, regardless of part and temperature variations.
  
  One other item was brought to my attention yesterday by
  Preston Brown that I should have included in my original
  posting here.	 While most of us recognize that comparing
  ram cards to a handful of dynamic ram chips to plug into
  your PC is apples and oranges, it may be more interesting
  to compare the HP48SX cards with cards for other products,
  like the Atari Portfolio, the Poquet, the NEC Ultralite,
  etc.	I believe you will find that the prices on the
  HP48SX cards are not at all out of line.
  
  Steve 
  "I claim all disclaimers..."
  
  the non-HP48SX cards
  
  From prestonb@hpcvra.CV.HP.COM Fri Mar  1 17:00:00 1991
  From: prestonb@hpcvra.CV.HP.COM (Preston Brown)
  Date: Thu, 17 May 1990 17:26:53 GMT
  Subject: Re: Memory Card: Give Us *True* Facts!
  Organization: Hewlett-Packard Co., Corvallis, OR, USA
  
  When the RAM cards detect that voltage is to low to operate they 
  clamp the address lines to ground.  This clamping is done by turning 
  on the output drivers of a custom chip included on the card.	The 
  clamping current is speced at 2mA min at the Vol output level.  Since 
  the 48 can be trying to drive the line all the way high even more 
  current is typical.  10mA per fight is not uncommon with totals of 
  several hundred mAs.
  
  The VDD power supply is regulated at 4.1 - 4.9 with typical 
  parts at the low end (4.3).  The power to the cards is switched
  thru a transistor, creating up to a 0.1V drop.  Standard Epson
  cards have a significant chance of seeing this voltage as 
  to low and shutting down.  We have seen cards do this in the lab.
  When it occurs the calculator locks up with VDD pulled down
  to about 2.5V and 250mA being drawn from the batteries.  This
  current drain greatly exceeds the ratings for the power supply
  and can damage your calc.  The least that will happen is a loss
  of memory.
  
  Now, why didn't we regulate VDD higher?
  The 48 has two power supplies VDD at 4.3 and VH at 8.5.  VH
  cannot be regulated higher without exceeding the spec for
  our CMOS IC process.	VH is used as the + voltage for the I/O.
  In order to meet a +3V output level VH must be more then 3.6V
  above VDD.  (VDD is used as I/O ground). Our power supply
  system increase the battery life and reduces the cost greatly
  for the wired I/O.
  
  Preston