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DIFFERENCES IN RAM CARDS

DIFFERENCES IN RAM CARDS

By Mark Scardina

It wasn't long after purchasing my HP 95LX that the desire for more file space welled up to the point where a RAM Card was the only item that would satisfy it. Having read HP's warning about a significant shortening of battery life if non-HP cards were used, I hesitated in considering other sources, but it became apparent that even if HP was right, I could buy a lot of batteries for the difference in price.

Memory Card Graphic

 I did settle on a non-HP card and experienced no significant change in battery life. Was this a valid warning or a ploy to convince you to buy HP? Since WESCON (the annual electronic component show) was in my city this year, I took the opportunity to investigate. The following is a compilation of my discussions with the major card manufacturers.

RAM CARDS AND BATTERY LIFE

The RAM Cards that are available for the HP 95LX are all "low power." RAM Cards can be thought of as operating in 3 different modes with the 95LX. When the 95LX is off, the RAM Card goes to sleep, drawing less than .01ma (milliamp) of current from its built-in battery. When the 95LX is on but not accessing the disk, a RAM card draws 1 - 1.5ma of current due to the 95LX polling the Card's address lines. The RAM Card draws 50ma when accessed.

Epson, the manufacturer of HP's cards, added an additional chip to their line of low power cards and created a new ultra low power RAM Card which draws only .25ma when in the idle mode. This was done with a gate array which basically "closed the door" on the polling activity, thereby reducing the load and the resulting current drain.

This is a unique design; therefore, HP's claims are valid. However, the question that remains is that while this is an 80% reduction, what is its impact on battery life?

Let's look at how the HP 95LX uses battery power independent of the RAM Card. When the 95LX is on but idle and the serial port is not active, it draws 30-40ma. If FILER or COMM is open, unless the serial port is turned off using the serctl /o command, the 95LX idles at 40-50 ma. The 95LX draws 150-200ma when computing. Finally, when off, the 95LX draws 0.79ma. (Graphics-intensive applications such as TigerFox take significantly more amperage to run).

One can expect approximately 2000 ma-hours from a set of alkaline batteries until the low battery warning appears. Therefore, by dividing 2000 ma-hours by 30-40ma that the 95LX idles at, we can guess that the typical user will get roughly 60 hours of idling time (HP 95LX on) from a set of batteries. In that 60 hours the Epson Card saves about one additional milliamp per hour, for a total of 60ma -- less than 1/30th of a set of batteries.

THE BOTTOM LINE

That means you will save one pair of batteries for every 30 pairs using the Epson/HP card! Compare this to the 10 milliamp difference between keeping FILER and DATACOMM closed (or the serial port off with the serctl /o command) and you will find that you save one pair for every 3 pair used. Now that's significant!

DANGER -- SAFEGUARDING THE FILES ON YOUR RAM CARD

One very important battery is the one in the RAM Card. When the HP 95LX is on and the RAM Card is inserted, the AA batteries or the AC Adapter power the card. While the 95LX is off, the RAM Card's battery keeps all of your files intact. Unfortunately, the card low battery warning system on the HP 95LX is not an early one. Therefore, please follow this advice: Change your card battery every 8 months.

If you ever see the card low battery warning, do not remove the card until you have backed up all of your files and you are ready to change your battery. Do not turn the 95LX off or let it timeout. (Press a key every 5 minutes.) Plug it into its AC Adapter if possible. Do not remove the AA batteries when you have a bad card battery as this will eliminate your files. The backup battery in the 95LX does not send power to the RAM Card.

The lithium batteries used by RAM Cards have a 5-10 year shelf life, so you can keep a few spare batteries for emergencies. And it's a good idea to set an appointment and alarm for your next battery change.

In looking to purchase a RAM Card it is important to make sure it conforms to the PCMCIA 1.0 standard. Therefore, if you want the most efficient card on the market, buy an HP or Epson. However, if your card is more than a few dollars cheaper than the HP card, it will take hundreds of batteries to offset the savings.
 
 

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