I suppose you have studied the list of registers and want to know in which order they should be set up and to what values?
The five most basic registers would be the 16-bit frequency, waveform and 16-bit ADSR settings. The ADSR usually only needs to be set once unless you want to change the sound between notes. The frequency obviously needs to be changed for every new note, and the waveform is the last bit to toggle on/off for each note.
I don't know to which memory address or I/O port you have mapped your SID chip so I will give examples based on the default location in a C64 = $D400, decimal 54272.
First we turn on the volume [$D418] by POKE 54296,15. It is four bits wide. Honestly I can't remember where the upper four bits would go, probably into void.
Then we set the ADSR. First byte is Attack + Decay. A value of $58 would mean an attack period of $5 and decay $8. Look up in the datasheet what those correspond to in micro seconds. POKE 54277,88 [hex $58]
Sustain keeps the note playing, let's set it to $A and a final release time of $9 = $A9 = decimal 169. POKE 54278,169.
Now it is time to set up the frequency. The datasheet has ready calculated values for a well tempered scale. Otherwise you can calculate your own using a formula. For this practical purpose we can set the frequency to any arbritrary value. The SID chip just like the 6502 is little endian, so the low 8 bits go into the first byte followed by the high 8 bits. A frequency value of $1234 thus would be stored as POKE 54272,52 (hex 34) followed by POKE 54273,18 (hex 12).
Finally, we choose a waveform. You have four basic ones to choose from, plus a couple of mixed waveforms. For keeping the simplicity, we use sawtooth that does not require setting up any other registers: POKE 54276,33
It can be worth looking closer at the waveform registers:
xxxxxxxN = toggle gate bit. When set to 1, the sustain will keep sounding. 0 will start the release phase, letting the note go away.
xxxNxxxx = select triangle waveform
xxNxxxxx = select sawtooth waveform
xNxxxxxx = select pulse waveform, requires setting up pulse width as well
Nxxxxxxx = select noise waveform
You saw I skipped three bits, which deal with synchronization, ring modulation and so on. You can read more about those in the datasheet or elsewhere. In order to understand how the SID chip produces sound, they are not required to know.
So, we got a somewhat shrill note sounding. POKE 54276,32 to let it go away.
As Bill mentions above, if you want to play a tune it is a good idea to set up a frequency table and use DATA statements to select notes from the frequency table. Then you would read pairs of note index and duration from the data statements, look up the exact frequency, set up registers and play the note. You use a FOR loop to determine when to fetch the next note.
By the way, POKE 54296,0 to turn off the volume alltogether.
Besides I have no idea if you can access your interface from TI (Extended) Basic or are forced to use TMS9900 assembly. Hopefully you know your way around that, it is a field I can't help with.
Thanks for the tip on pulse rate, I'll check it out when I get a chance. I just bought the Compute! Music System Book from Ebay so perhaps that will shed some light on the situation.