of Microprocessors

OrHER INPUT METHODS
335
1111111010101011
0011001000100011
1100001010000011
000000100000001
(0)
0001110001001011
1000000110010010
0110111001000001
0101101101011001
0110000111110110
1111010111010001
0000110110001111
0011100110001011
0100100010100101
0100111011101100
1111011111101001
1001101010001100
0001110101010111
1100101000010011
1111110000101111
000110100000001
{El
Fig. 10-10. Some B-bit feedback shift register sequences (cont.) (D) Switches =
10000001. (E) Switches = 00011101. This is the longest possible
sequence using an B-bit register (255 bits).
small number of stages can create a nearly infinite number of different
patterns ranging from highly structured to virtually random. The sequence
length (number of clock cycles necessary to cause the sequence to repeat)
varies from just 2 to 2 N -1, where N is the m;mber of shift register stages.
From this vast array of sequences, Fig. 10-10 S:10WS a few of those possible
with an 8-bit register.
The Muse
At least one interesting device has been marketed that is based on the
feedback shift register principle. It is called the "Muse" and is advertised as a
music composition machine with which the user, by setting several levers
and swItches, controls a sequence generator, WhICh 10 rurn controls a single
oscillator to produce notes.
A simplified block diagram of the device is shown in Fig. 10-11.
Thirty-eight different digital signals are generated by several counter stages
and a 31-stage shift register. These signals along with constant 0 and 1 are