[sdiy] CMOS chip questions

[Scott Nordlund]

74HC is usually fine.  I prefer 74HCT since its inputs are TTL compatible.  If you need something faster, use 74AC.  The problem with diode logic (I guess you're using diode resistor logic?) is that you can't really chain stuff together.  The speed depends on your choice of diodes and resistors as well as whatever you're driving.  I believe TTL circuits prefer pull-up resistors rather than pull-down (doesn't matter with CMOS), so this may limit your options in some cases.

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> Date: Fri, 17 Jul 2009 16:11:11 -0700
> From: dixon at interchange.ubc.ca
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] CMOS chip questions
>
> I'm currently redesigning a matrix keyboard circuit, and I've got a couple
> of general questions for the "gurus" about CMOS.
>
> First, presuming a 5V supply (from a 78L05, for example), is there any
> reason NOT to always use the 74HCXXX version? The advantages are speed,
> very low power consumption, and output data levels exactly the same as the
> supply. Is there any downside which would justify/demand using the CD4XXX
> version of the same chip?
>
> Second, I'm finding that I need the odd AND or NAND gate in my circuit, and
> I'm leaning towards simple diode logic (without or with schmitt trigger
> inverters, respectively) to save board real estate. Multisim simulation
> tells me that this should work swimmingly. Are there any pitfalls I should
> be aware of?
>
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