Hi folks! Yesterday, I downloaded the English version of VIC-20 Programmer's Ref Guide, and to my surprise, I found something I've never seen before. In the chapter about 6522 VIA, the user port also is described and after discussing the CB2 output from the 6522, the PRG says: > MORE MUSIC FOR THE VIC > Now that you know about the USER PORT, there is a little surprise left. > Up to now, the VIC has had 4 musical voices...three music registers and a > white noise register. By connecting a small amplifier and speaker to the > USER PORT, and doing a little programming, you can get another musical voice. > THEORY > Most music is made up of square waves of different amplitudes and > frequencies. One of the functions of the 6522 chip is to generate square > waves through the CB2 line. If we connect the CB2 line to a speaker, we > will be able to hear the square waves generated by the VIC. > NOTE: Connecting a speaker directly to CB2 may damage your VIC. You must > connect the speaker through an amplifier to protect the VIC. > PARTS NEEDED > 1. Small battery powered speaker/amplifier > 2. User Port Connector (12 position, 24 contact edge connector > with .156" spacing > 3. Wire > CONNECTING TO YOUR VIC > 1. Wire the GROUND of the amplifier to the GROUND of the USER PORT (pin N). > 2. Wire the SIGNAL of the amplifier to the CB2 output of the USER > PORT (pin M). > You are now ready to add your other voice through a BASIC program. and then follows instructions on how to set the registers and a BASIC demo. According to these instructions, the VIA can produce 256 notes per octave, in three different octaves: 500000 Hz Where D1 = 8 when D = 15 (POKE 37146,D) FREQUENCY = --------- D1 = 4 when D = 51 (C+2)(D1) D1 = 2 when D = 85 This means a range from 243 to 125000 Hz, if I'm not totally wrong. Compare this with the three regular square wave voices, ranging from 33-4329, 67-8659 and 135-17320 Hz (with PAL clock, slightly different values for NTSC). Did anyone ever try this? It sounds just as bisarre as the SOUND IN on the SID chip (which I also never tried). I've got a spare user port connector and could probably hook up a mono RCA plug for testing. Mmm. Can one auto-detect if the CB2 line is connected to something, and select music player routine based on that (for demo purposes etc) ? /Anders Carlsson - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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