23 Aug
2014
23 Aug
'14
8:32 p.m.
On Sat, Aug 23, 2014 at 9:55 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
Without any termination resistors, an undriven bus line should nonetheless
be interpreted (by the 7404) as high, so the D2 LED should be on.
It would appear something else is pulling it low (or something is wrong
with the 7404/LED).
Not in this case.. and I mentioned why a few posts back, but I don't blame
you for missing it.
The non-gate side of the LEDs are connected to Vcc (5V), rather than Gnd.
So if the 7404 input is L, the output is H and the LED is +off+ (5V on both
LED terminals, no current). If the 7404 input goes H, the output is L and
current sinks from the Vcc line through the LED to the (low) gate of the
7404.