Volume 2, Number 4 – September 1982

Page 21 of 36

With regard to dats retention, the following pointe should be nated:

Data corruption 15 more frequent while Vee is rising (during power-up) than while “Vee i= dropping (during power-down) however it can happen during e1ther transient phase. Corruption usually takes the form of one or two bits in a few (apparently random) Locations being set high.

The causes are many and various but, as Paul Anderson points aut, are predommantly due te the unpredictable behaviour bf the Bus control «:gnaln during the transient phase of pomer-up and power-down. Corruption is not always easily Selected, we ourselves une a cheek-summing routine after having initialised memory contents with the pattern Aahex Sohex.

Those readers whe have purchased our memory boards may have wondered why on receipt your board is full of AA SS. I you Feally want to be smart you can run this pragram at 2000hex “by Selecting IC 11-1? to block 2 Gf you did not overwrite 48 in your enthusiasm 0 use the board).

To overcome this danger of corruption, wo developed a fast smitch circuit to disable read and write lines whenever Vcc falls below 4.6 volts. (see diagram) The circuit is based about a programmable zener (IC 1) set to 4.6 volts. The reason we use this particular device in preference to a normal zener is due to the fact that its dynamic slope impedance is only 3 ohms. as a reault, as soon as Vee rises above the programmed zener voltage (4.60) the zener draws current through TRI’s base, switching TRI

12 15 switched on whenever Vcc is above 0,6 volts and below 4.4 volts and while switched on pulls the commoned enables of the tristate buffers low, thus disabling all read and writes. The circuit switches in under 2 micro seconds.

T hope this information wll Rave been of some interest and, perhaps. use to your readers who intend utilising these Belighttul chips. Non-volatility is an asset that, once. gained, forces one to think how on earth one survived without it.

Lastly, a5 a concession to Micro Power readers, we will offer the HMSI16LP-5 UI50nS access time) at £4.50 and the Toshiba TCSSI7AP (150nS access time) at £4.95 up until January 1983 to readers who enclose the cut-off section from our advert. in Micro Power.

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

Page 21 of 36