Homebrew Logic Analyzer

I want to build a logic analyzer. It must beable to detect upto about 5mHz. It doesn't need to go higher than that, but it would be nice. I know it will be complex, but i need one(i don't have the money to buy one. I would use the parallel port on one of my laptops, but that would only detect upto about 100khz! Any ideas? I was thinking of using a PIC. Would the I/O's be fast enough?

How many channels in your analyzer?

At least two. More would be nice, but it isn't mandatory.

You are going to run into some practical limitations on I/O speed and memory storage. think about how you would sample the input port. how fast can you read the value and save it away. how many samples can you save before you run out of memory?

then you need to consider triggering. what kind of triggering do you want? the more complex, the slower it will be.

most people that look at doing this are quickly drawn to using some sort of programmable logic device like an FPGA and fast static memory. a microcontroller is used to dump the samples and trigger data to a PC for analysis and display

I have looked at doing this with a renesas chip that supports DMA and external static ram but it didn't look like it could go that fast. my initial tests were not encouraging.

I think i am going to buy one....