BigDumbDinosaur wrote:
CMOS input current draw is only significant during switching from one state to the other. Plain MOS inputs present some DC loading, as well as capacitance, which means fanout requirements using 74LS logic will be higher than when using one of the CMOS families.
Not sure I follow you, BDD. If you mean 74LS (or any family) will have more difficulty driving the inputs of an NMOS 6502 than the inputs of a CMOS 6502, then the statement seems to miss the mark. In both cases the DC loading amounts to leakage current only. Although the input leakage current for WDC's CMOS 6502 is lower than (for example) Rockwell's NMOS 6502, even the latter draws a maximum of only 2.5
micro-amps -- which is negligible, wouldn't you say?
Quote:
The W65C02S is the better MPU choice, due to a number of electrical characteristics (higher fanout being one of them—I'll get back to fanout in a minute) but also because it fixes implementation bugs present in the NMOS part. [...] Beware of 65C02s sold by some vendors that are not WDC parts! Many are old Rockwell pulls rated for one or two megahertz.
"Beware"
?!! Okay, sure; the W65C02S is a better choice for knowledgeable folks whose priority is maximizing performance, but the main goal of most novices is a trouble-free experience with their first project. That being the case, the old-tech CMOS 6502's are probably a
better choice than the WDC part. That's because of the WDC's potentially troublesome fast edge rates. There's nothing tainted or substandard about CMOS 6502's from other manufacturers. No, they're not presently in production. Yes, they include the bug fixes.
Quote:
74HC is actually fairly old technology that peaked in the late 1980s and is not recommended for new designs.
Scot, your project will have sockets for the IC's, and that makes it easy to experiment with different logic families initially and in future. It's your own choice whether you want to choose the faster logic families as your starting point. BTW, paraphrasing Mark Twain, I think reports on the death of 74HC have been greatly exaggerated!
cheers,
Jeff
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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
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74AC is readily available in PDIP as well as SOIC, and is current production with several vendors (e.g., NXP and ON). 74HC is actually fairly old technology that peaked in the late 1980s and is not recommended for new designs.
).
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After many years (37 of them, to be exact) of writing eight bit 65xx code, I fully appreciate the "economy of speech" that is possible with the '816.[/quote]
But what would be helpful is if you'd mention the source of your information. Are you expressing your own opinion that 74HC is unsuitable, or have you seen manufacturers' notices that suggest 74HC may become difficult to obtain? (When a manufacturer's data sheet says "Not recommended for new designs," it implies that production of the product may be discontinued.)
