At 04:00 PM 2/12/98 -0600, you wrote: >Has anyone built a PIC-based digital O-scope / logic analyzer ? > Hi Dan, I am working on essentially the same project that you are. I have a prototype finished and I am in the process of getting it to work. Because I am currently a college student with very little free time, this is taking longer than one might expect. My design is quite simple and consists of a 40 MS/s ADC buffered by a high speed op-amp. The output of the ADC is captured by an SRAM (128kbit x 8). The clock is provided by a little can type oscillator, and the address is derived from a pair of 8-bit synchronous fast counters (74F579). A PIC controls when sampling is started/stopped and also allows a PC to read out the contents of the SRAM and clear the counter. Communication is via bi-directional EPP parallel port. I have had the prototype together for about a week and have had only abo ut 2 days to actually work on it. It is giving erratic output, which I think is due to some type of synchronization problem where either the SRAM is being programmed while the output of the ADC is undefined or the parallel port is reading the SRAM when it is not ready. I will continue to work on it and keep the piclist updated. I would encourage you, Dan, to also try your design. I am willing to help with component choice/ etc. As for trigger, I was going to just simply continuously sample (well, until 64k or whatever) was full, and then only display past a trigger point (similar to what commercial DSO do). This method also allows pre-trigger viewing. The only problem is that I can only sample in chunks of (maximum) 64k (16 bits of address) and the PC takes at least 32 milliseconds to read this out. This would give a maximum sampling duty cycle of 5% at 40MS/s or 40% at 5MS/s, the minimum rate for this ADC. This is a problem which you might try to overcome. Special triggering circuits might allow special functions, though, such as repetitive sampling to get very high effective sample rates on repetitive waveforms. Good luck, Sean +--------------------------------+ | Sean Breheny | | Amateur Radio Callsign: KA3YXM | | Electrical Engineering Student | +--------------------------------+ Fight injustice, please look at http://homepages.enterprise.net/toolan/joanandrews/ Personal page: http://www.people.cornell.edu/pages/shb7 mailto:shb7@cornell.edu Phone(USA): (607) 253-0315