Trying to make an ALU? Search for gate level schematics for the 74181 4-bit ALU, it's been copied to death by now so I guess that means it's pretty optimal

That's the lazy man's way of writing circuit.

I remember you... a couple of years back there was another bunch of EE students on LYN and we had threads like this too. You were at Newcastle, right? Graduated already... makes me feel even more like a dinosaur.

phew, the thread grew two whole pages overnight.

Designing with NAND gates is a higher level of abstraction and usually gives you a ballpark figure of how many transistors are going into your final circuit. Furthermore, a NAND gate's electrical properties; fan-in, fan-out, propagation time, etc. are known quantities. If you go all out full custom, be prepared to run test after test to make sure you don't suddenly get an oscillator instead of an ALU (an exaggeration, I know ).

Most of the discussion in this thread falls under Electronics Engineering. Digital Logic is usually a first year course after which students promptly forget about it. That's until they go into VLSI (Very Large Scale Integrated Circuits) design later on, and then they scramble to re-learn it again.

Software Engineering is not just all about programming; you'd be learning about project management, high-level design, algorithm design, formal verification and other deep stuff. I'd say it falls somewhere between Computer Science and IT.

You stick em on the board then stuff the whole board into an oven and cook it. Surface tension will pull the part onto the solder pads nicely. Inspect with an X-ray or ultrasound to make sure there aren't any shorts. Like baking a cake (except for the x-ray part ).

Never used verilog and VHDL lessons were 8 years ago, but I'll give it my 2 sen...
address is 6 bits wide, but memory depth is only 35 words, what's up with that?
you're using the same counter as the address and data input? then address 0 will never be accessed and the first data will always be 1.
you can make your controllers easier by having an extra 1 address bit and then using the most significant bit to flip EN to enable RAM bank number 2, but that'd only work if you let the counter run the full length of the addressable range (0-63).

This post has been edited by silkworm: Dec 4 2005, 12:29 PM

any particular reason why your dataset/memory depth is not a power of 2 other than "it says so on the question paper" ?
can try an oddball addressing scheme, like using gray codes instead of a straight binary sequence, but that'd only complicate things more

Half-right.
It's actually a voltage doubler circuit, which is equivalent to "two halfwave rectifiers in series". In the textbooks I looked at, the circuit is almost always introduced in the diode section, just after full-wave bridge rectifiers. No idea why he'd want to series two caps on each "side' though, that leads to smaller capacitance as you've mentioned.

If you don't need a whole lot of accuracy or linearity, then why not DIY? 5-bits is pretty do-able with an R-2R ladder.

Alternatively, a good ol' 8-pin PIC with 6 IO pins, 5-pins for your parallel input and one pin for the output, just nice! It's extremely easy to knock together a bit-banged PWM output, then just low-pass filter the output pin and you have your analog output.

Finally in the "overkill" department, a FPGA could do the job. FPGAs outputs usually have about 3-bits of programmable drive. Chain together 4 pins (I think) to get your full range of outputs. This solution sucks a lot of power though.

In situations like these, look at the tools being used in measurement. An Ohmeter is just measuring the voltage across the resistor after pumping in a known current. If the DAC resolution is not high enough, or the voltage scaling not large enough, then the result of the measurement is bound to be erroneous. Furthermore, if the resistance of the ground wire is less than the resistance of the probe leads, then the readout is also definitely wrong.

Fair enough. Was it a handheld unit or a bench-top? What does the specification for the multimeter say about the resolution and accuracy? For measuring something in the milli-ohm range you should probably be using a RCL meter with Kelvin clips instead of a two-lead, contact probe multimeter.

Measuring Resistance (epanorama.net)

Congratulations! You've sure earned it.

They're not in Penang, but try Silvtronics, based in Old Klang Road, KL. Their prices on the website are in USD, but if you e-mail them they'll quote you in RM. It might seem pretty expensive at first, but they're probably the cheapest for making 1-4 piece runs.

While obviously not competitive to the coal-makers from Intel or AMD's stables, FPGA-based "soft core" CPUs are capable enough to go up against lower spec ARMs and MIPses. And that's a huge piece of the pie right there.

And that's how everything is supposed to start. I guess the dotcom bubble mentality of "think big, start big, get bigger" is still lingering around.