Wave Selector

There are twelve bits each with four inputs for the different waveforms connected as follows:

• Pulse: each bit is connected to the latched output of the pulse adder;
• Noise: the lower four bits are grounded while the others are connected respectively to the bits 0, 2, 5, 9, 11, 14, 18 and 20 of the LFSR register;
• Triangle: the LSB is grounded while the remaining bits are connected to the triangle xor outputs;
• Sawtooth: the lower eleven bits are connected to the triangle xor outputs while the MSB is connected to bit 23 of the oscillator, directly in the 6581 and through a latch in the 8580.

An interesting thing to note is that in the 8580 the upper eight triangle selector transistors are narrower than the others, meaning more resistance, while the lower four and the sawtooth ones are slightly wider. In the 6581 all selector transistors are the same size except for the pulse ones which looks sligthly longer (but it might be just an effect of vectorization).