RS-232 Tx / Rx monitoring LEDs?

Brian L. Stuart blstuart at
Thu Aug 20 12:35:37 CDT 2015

On Thu, 8/20/15, Mouse <mouse at Rodents-Montreal.ORG> wrote:
> Maybe _rated_ current, but, even there, I don't think so (my TTL
> doc hasn't been unpacked yet, or I'd go check, but I'm fairly sure
> they are generally specced to sink more current to GND
> than source from Vcc).
It so happens I have a TTL handbook to hand at the moment.  From
the 1985 TI TTL data book:

        Ioh   Iol
7400   -0.4   16
74H00  -0.5   20
74LS00 -0.4   8
74S00  -1     20

all in mA.  So as rated, TTL devices can sink a solid order of
magnitude more current than they can source.


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