With regard to dats retention, the following pointe should
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.