CMOS logic level range

Isn't this a datasheet thing? D from BC

level 1 is 4.5V to Vcc 0.5V, okay?

The "official" specification is usually...

"0" = 0.7*VDD

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

The not-so-official specification is usually...

"0" = 0.7*VDD

"linear" = 0.5*VDD

:-)))

Sane people don't do "linear" with off-the-shelf CMOS ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

Good. So if someone wants to sue me I could then claim immunity based on the grounds of insanity ;-)

That will certainly work, but if any logic level is very far off the rails (a volt maybe? less?) the chips will draw excess current and run down your battery.

John

So, I guess the HCU04 isn't "off the shelf"? ;-)

and, BTW, I had thought that 0 = 2/3 Vdd. (.67)

Thanks, Rich

That doesn't include taxes ;-)

typically cmos high is 2/3 of VCC and above, read a few datasheets.

with a 15V supply 5V would be low :)

Bye. Jasen

Depends on the logic family. Traditionally (eg the old CD4000 series chips), you can power them from anywhere from 3V to 15V, & a logic '1' is anything above 1/2 the supply voltage, '0' is anything below that. For newer CMOS logic families, they specified for all sorts of weird voltage ranges. You can find out for sure from the data sheet.

But as a general rule of thumb for any CMOS logic chip powered by 5V, you can assume that any signal above 2.5V will be treated as a '1', & that anything below about 1V will be considered a '0'.

Again, if you're doing anything critical, you need to look up the data sheet.

I believe 2.5V is wayyyyy too low for a Vcc of 5V unless you're warming up the parts. ;-) I'd keep it at .7Vcc (.8 *Vcc for Schmitt trigger inputs) to be safe. IOW, 3.5V is the minimum.

You've obviously grown up with TTL compatible CMOS parts. ;) Go check the 4000 series spec's.

Lionel, YOU need to re-read the data sheets.

...Jim Thompson

You must think they all are. ;-) I'm not trying to be rude, but maybe you should look again. Vih is usually at least 3.5V on CMOS, anything below that and you are gambling. 2.5V is waaaayyyyyyy toooooooo looooooowwww for CMOS inputs. ;-) PIC chips want 4V minimun on 5V Vcc (.8 * Vcc).

I will add that for the PICs, the pins that have TTL input buffers (most of them) only require 2.0V (4.5V < Vcc < 5.5V). The official formula is (1.25

• Vcc) + .8V, but they make a special case for 5V operation. But I believe this is a special case and not consistant with normal CMOS specifications. The Schmitt trigger inputs want .8 * Vcc.

That's the Typical spec and certainly wouldn't be something to recommend as a rule of thumb IMO. I'm going to stick with the value in the column next to that one that says (Min 3.5V).

I do? I'll admit that it's been at least 15 years since I last looked at a 4000 series data sheet...

Well, according to Motorola (), at a Vcc of 5V, (@25c), a logic '0' = 0-2.25V, & a logic '1' = 2.75V -

Maybe your memory's getting a little rusty too, eh Jim? ;^)

Sure, but they're designed to switch at Vcc/2.