On (20 Feb 95) [EMAIL PROTECTED] wrote... > Date: Mon, 20 Feb 1995 18:26:31 GMT > From: "Brian Gaff Sam Dept." <[EMAIL PROTECTED]>
> Hang on though, a CMOS chip has less drive too, and that is a > problem on sam. Look what happens on the 2up? What happens on the 2up? On my original 3up that spawned the idea of the 2up I can happily run 2Megs ram and a COMMS interface straight off the back of a standard twin internal drive sam... No loading problems at all! Any way I was speaking of a Sam motherboard optimised for a battery powered robotics controller not for normal fully expanded everyday use:-) Though I don't think the Z84C?? range of chips have a much reduced drive capability, it's more different drive characteristics! Eg I believe NMOS z80 provides drive at near identical TTL current levels ie logic 1 output can only source a few hundred micro-amps and a logic 0 output can sink upto a few mili-amps... which would be naff for driving capacitive loads of long data/control buses because it'd have very little drive to charge the bus capacitance to logic 1 but have more than enough current sinking ability to discharge the bus capacitance! Whilst CMOS output stages use a symetrical Complimentry MOS transitor pair and thus provide equal sink & source capability! One consiquence of this is that even if the logic 0 sink ability was half that of the NMOS equivilent the logic 1 source current would be MANY times better than the NMOS version... So a CMOS z80 would be more reliable on a bus that's a bit too high a capacitance for a NMOS z80! In theory anyway;-) Regards Johnathan. ... In theory, theory and practice are the same. In practice, they're not. -- |Fidonet: Johnathan Taylor 2:2501/307.9 |Internet: [EMAIL PROTECTED] | | Standard disclaimer: The views of this user are strictly his own.
