On Thu, Aug 20, 2015 at 10:54 AM, Paul Koning <paulkon...@comcast.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.

Not for true (bipolar) TTL.  See the specs for the 7400, 74LS00, 74S00:
    http://www.ti.com/lit/ds/symlink/sn74ls00.pdf

          Ioh(max)  Iol(max)
7400      -0.4      16
74LS00    -0.4      8
74S00     -1        20

CMOS for comparison:
    http://www.ti.com/lit/ds/symlink/sn74hct00.pdf
    http://www.ti.com/lit/ds/symlink/sn74act00.pdf

          Ioh(max)  Iol(max)
74HCT00   -4        4
74ACT00   -24       24

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