September 1982, Volume 2, Number 4

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CMOS Battery-backed RAM Update

Micracede (Control) Limited

Having read Paul Anderson’s excellent article: ‘16K CMOS Memory Extension for the Nascom 2 Main Board’, I would just ike to mention a few points of interest.

Experience gained in manufacturing the 32k_—CHOS Battery-backed Board (see aur advert. – will the Editor forgive us thiz ‘plug’?) has taught us the following lessons with regard to the standby current of these amazing @enory chips. (imei 16).

1. The standby current is extremely temperature dependant and for a particular memory chip this may vary aver a ratio of 1000713 we consider an average Of 1. micro-amp per degree Centigrade over the zone 15 to 25 degrees C as about typical for the standard ‘P’ series.

2. The best standby current is obtained by pulling the address, read, write and chip select signals up to V standby while in the ‘standby mode. This obliquely hinted atin the specification “sheets for these devices. This 15 most Conveniently done using 10K DIL resistor networks. Without these pull-ups the ‘in-cireuit’ standby current. will often reach over 150 micro-ampe.

3S. In order that the pull-up scheme works, it is wise to use trastate buffers on these lines. However, this introduces: yet another current eink, namely the leakage of the output transistor pairs in the tristate drives.

We use 7415126 quad tristate non-inverting buffers with active-high enable. Reware of the standard 74126 TTL part, as this has a wicked diode between the cutput pair and. the Vee to catch the unwary (me!). Also the 5.6.5 version of the 7ALS126 seems to be leakier than other manufacturers.

4, If you want really long data retention periods the standby currents af the ‘Le’ versions are of at least an order of magnitude better.

The “LP versions are functionally identical but have paused a special ‘low standby current’ test during the final stage Of manufacture. The slightly higher price ts well worth the cost in terms Of this performance in our opinion.

5. Just recently the Toshibe equivalent device (TCS5I7AP) has dropped in price to comete with the Hitachi chip. The Toshiba chip does seem to be far superior in all parameters and our own tests would seem to verify the manufacturers claim.

This is an OCR’d version of the scanned page and likely contains recognition errors.

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