On 9/15/2010 1:28 PM, Dan Roganti wrote: The parts list below the schematic says LS or HCT is acceptable. For new designs, I thought either 74HC or 74HCT parts were best. My limited understanding is that their power draw is lower, accept both CMOS and TTL level signals, have a wider power supply range, have high sink/source ratings, etc. Note that I'm just regurgitating what I read online, I really have no experience with this stuff. The main point is that the Amiga has analog RGB outputs, and separate horizontal and vertical syncs. I need those syncs combined into a composite signal. It goes down to 15khz when you feed it a COMPOSITE SYNC signal. It you give it separate RGBHV signal(which comes out of the Amiga on the DB23), it only goes down to 30khz, hence my problem. I'd like to attach an LCD to the amiga. The output from my amiga is usually 320 x 240, and so two things have to happen: 1> 15.7khz has to be doubled to something in the horiz freq range that the monitor can handle. 2> 320 x 240 has to be scaled to something the monitor will take natively, likely just 640 x 480. While this might do the appropriate pin-changing to get the amiga video signals onto a standard VGA connector, it does absolutely nothing for affecting the horiz sync rate which is problem numero uno! Thanks Keith

Assuming you just need a single XOR gate (which is normal for this), then you could use the 4 NAND gates in a 74x00 to make one. The schematic is well-knon, but in case you've not coem across it : ---------+-----------|\ | | >o---+ | +---|/ | +-|\ | +--|\ | >o--+ | >o---- +-|/ | +--|/ | +---|\ | | | >o----+ --------+-----------|/ If you need an XNOR gate, I think you can use a similar circuit with 4 NOR gates (e.g. all the gates in a 74x02) Also, inverting an odd number of the 2 inputs and output (that is, a single input, the output, or all 3) will change an XOR to an XNOR or vice versa, while invertian and even number (both inputs, or one input and the output) ahs no effect. . -tony