> On Aug 20, 2015, at 11:58 AM, Mark J. Blair <[email protected]> wrote:
>
>
>> On Aug 20, 2015, at 06:27, Paul Koning <[email protected]> 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.
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
