[sdiy] Shift register sequence period

[Phillip Harbison]

Tim Stinchcombe wrote:
> *Because* of the inverting action, I don't think the circuit
> needs any kind of 'kickstart' - there is nothing like that in
> either the Doepfer module (and it works all the same!)

The purpose of the RC network and extra XOR gate might be to
force the sequence into a predictable starting state; however,
if that is the intent then the RC network should be buffered
by a Schmidt trigger to achieve a reliable result. On second
thought, perhaps the designer wanted the input to that XOR to
be unpredictable making the startup state random. In either
case, a diode in parallel with the 1M resistor is a good idea.
I've used these shift registers but only to calculate CRCs on
data packets and in rare cases as a digital delay line.

-- 
Phil Harbison