6502 CPU has four instructions which they have four strobes. STA $2000 is single strobe. STA $2000,X is double strobe. ASL $2000 is triple strobe. ASL $2000,X is quad strobe. It looks like one strobe turns on tape cassette or speaker. It needs second strobe to turn off tape cassette or speaker. It means that you want to toggle the on/off switch. You use STA $2000,X which it has double strobes. It can turn on and off tape cassette or speaker during two cycles. Am I correct? It is what I understand that it only takes one cycle to turn on tape cassette before it has to take second cycle to turn off tape cassette. Is on/off switch useful during two cycles for communication through serial port, Disk II Logic, and other I/O devices? Is ASL $2000,X useful for tape cassette if you want to turn on and off twice as quad strobe? Bryan Parkoff "Bryan Parkoff" writes: > Is ASL $2000,X useful for tape cassette if you want to turn on and off > twice as quad strobe? No, because the frequency of the resulting pulse is way too high for an audio tape recorder to handle. Bryan Parkoff wrote: > Eric, > > Then, I don't understand what strobe is for to do with I/O. If you use > STA $2000, speaker will be turned on constantly without turning it off until > second STA $2000 has to be executed by turning it off, otherwise STA $2000,X > allows to turn on and off speaker during two cycles. Yes, but the question is: what is the application for a one-microsecond pulse on the speaker? Or two consecutive one-microsecond pulses? Although one might be able to come up with uses for short pulse streams, they would generally be more useful if coming from the STROBE output on the game port. In practice, most strobe uses require single pulses (for handshaking), not multiple ones. The fact that the 6502 can produce multiple pulses with a single instruction is a kind of curiosity with few practical uses. Generally, you want to toggle the speaker, leave it there for a while, then toggle it back. If you repeat this at an audio rate, an audible tone is produced. If you toggle the speaker at an ultrasonic rate, with varying duty cycle, then "arbitrary" waveforms can be produced from the speaker. (See my web site for SOUND.EDITOR and DAC522.) -michael New Applesoft BASIC interface for NadaNet networking! Home page: http://members.aol.com/MJMahon/