20 Aug
2015
20 Aug
'15
9:54 a.m.
On Aug 20, 2015, at 11:58 AM, Mark J. Blair <nf6x
at nf6x.net> wrote:
Ok, but when you refer to "drive strength" I assumed you were talking about
current, not voltage. By that measure totem pole outputs are pretty much symmetrical.
palu
On Aug 20, 2015, at 06:27, Paul Koning
<paulkoning at comcast.net> wrote:
Totem pole outputs have comparable drive strength in both directions, that's
precisely their purpose (to provide symmetric rise/fall times when driving capacitive
loads).
That's true for CMOS outputs. TTL outputs pull down much more strongly than they pull
up, which is why older designers are still in the habit of driving LEDs with active low
outputs even though active high outputs work just fine with modern CMOS logic. Look at
nearly any TTL datasheet, and note that VOL is much closer to ground than VOH is to VCC.