Cyclone Analogic Bass Bot Uživatelský manuál stáhnout pdf (Strana 4)

1 - IF power is supplied via an external 9 volt adaptor (which is regulated inside the

TB-303 to +6 volts) AND the power switch is turned on, then this will supply

VRAM via a diode, resulting in about 5.4 volts, which is fine for read-write

operations and data retention between these operations.

If there was no external power supply and the machine was running from

batteries, then there is no 6 volt regulator, and VRAM is driven via a diode

voltage drop from the C-cell battery voltage, which may be as high as 6.4 volts or

so.

2 - IF four C-cell batteries are installed AND either there is no external power supply

OR the power switch is off, then the voltage from the batteries (nominally 6 volts,

but it can be higher with fresh alkaline batteries) drives VRAM via a diode - so

the memory chips get about 0.5 volts less than the battery voltage. (0.5 volts due

to the very low current required to drive VRAM when there are no read or write

operations.)

With fresh alkaline batteries, each of which have significantly higher than 1.5 volts, both these pathways

may drive the VRAM supply above 5.5 volts, which is the maximum operating voltage of the original RAM

chips. However, they seem to work fine.

The VRAM voltage is sustained, for a short time, such as a day or so, by a 100uF (millionths of a Farad)

capacitor. (A capacitor is like a storage tank for electricity. It is somewhat like a battery, but it has no

particular voltage, such as 1.2 volts for a nickel-metal-hydride battery. The voltage rises and falls in direct

proportion to the charge which is stored.) Since the current consumption of the three standard memory chips

(when there are no read or write operations) is so low, this capacitor would slowly discharge over a period of

a day or two (or maybe more in cool conditions) and so keep the memory chips supplied with a high enough

voltage (probably 2 volts or more is sufficient, in practice) to keep their data intact.

In practice, depending on the self-leakage of the capacitor and the temperature and exact natures of the

original memory chips, this capacitor would retain memory contents, in the absence of C-cell batteries or the

machine being turned on, for a few days, and perhaps a week or more. The sole purpose of this capacitor is

to retain data while the user removed one set of C-cell batteries and installed a fresh set, without running the

machine from an external power supply.

As the capacitor discharged further, the voltage would be too low for the flip-flops to retain their states. So

when proper operational power is applied (5 volts or so, when fresh batteries are installed, or the machine is

turned on with an external power supply) they assume states which are unrelated to the states they were in as

a result of the last write operation. That state depends on the exact physics of each of the cell's transistors,

and some cells will tend to flip (binary 0) while others will tend to the flop (binary 1). We think of these

states the flip-flops wake up in, when a proper voltage is applied to them, as "random" since we can't control

them. Different brands of memory chip (NEC, Mitsubishi and Toshiba) have different kinds of patterns of

flip-flop states, and so no-doubt give rise to somewhat different types of "random" patterns.

The current consumption of the original memory chips is far too low to drain the C-cells in any time period

of interest. An alkaline C-cell has a capacity of about 7 amp hours. So even if the memory system drew 1

microamp, it would take 7,000,000 hours to drain the batteries, which is 800 years. The self-discharge rate

of C-cells is higher than this.

There are several problems with this original arrangement, for a normal TB-303 or a Devil Fish modified

TB-303 (if it had no lithium battery or other arrangements as described below, as was the case for Version 1

Devil Fishes in 1993-94):

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Cyclone Analogic Bass Bot Uživatelský manuál Strana 4

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