Re: cine sound board

> Yup! That's the part! Thanks David.
>
> So do you have the full specs on the part? This is the one I played with=
> in the
> past, the fact that it uses a "pseudo-random" generator is indicative of =
> a LFSR,
> since a noisy semiconductor is a truly random source.
>
> -Zonn
>

        The S2688/MM5837 ARE LFSR-based pseudo-random noise generators.

        I went to the UTexas library last night, and wasn't able to find a datasheet, but I DID find a functional block diagram in a reference called D.A.T.A. (forgot what it stood for)

        Anyways, the LFSR is 17 registers long, and the 14th and 17th bits are fed back to the "Exclusive Or Circuitry" block. All the bits of the LFSR are NORed together (zero detect.) The output of this NOR gate is also fed into the "Exclusive Or Circuitry" block.

        This is an MOS part, and takes 3 voltages (2 supply -- Vdd and Vss, and one control voltage, Vgg)

        The part has an internal ocsillator and clock driver to generate the clock for the LFSR. The 17th bit of the LFSR is send through a push-pull output buffer, and that is the noise output, so it looks like there is no integrator on the output.

        Vgg controls two "Test Gates" which are probably nothing more than MOS switches. There are two test pins (TESTA and TESTB) on the chip. It looks like when Vgg is high, TESTA is input to the "Exclusive Or Circuitry" block and TESTB is input to the "Internal Oscillator" block (Probably if you want to supply your own clock.)

        Anways, it looks like I have what I need to emulate this thing. If anyone can provide more detailed specs, especially about how that internal oscillator works (i.e. is it just one frequency, or does it vary in frequency) I'd appreciate it.

Joe
Received on Thu Jun 12 07:19:34 1997