Halt and catch fire is written by people who do not grasp technology well. But +5 is only used by the TTL and some CMOS gate families. Very little hardware still uses that voltage. -5 was as associated with ECL logic which was fast in it's time but very power hungry. It's possible you could capture a serial stream on a scope but in those days storage scopes were not digital. They were rare and expensive. Early MOS memory chips also used -5 for bias purposes, ie they required multiple power supply voltages due to the limitations of the transistors on those chips.

http://en.wikipedia.org/wiki/Emitter-cou...

Op amp chips typically have two power rails plus the 0V rail. E.g. +5V, 0V and -5V or +12V, 0V and -12V

It would be four LEDs, and it is not difficult to read and convert to hex in your head.

It doesn't necessarily have to be a +5 V. -5 volts can mean the same thing. TV shows take lots of liberties. Far to little information to tell you anything else.

An alternator? Indicator that the voltage would change direction, and therefore polarization

i was watching the amc show 'halt and catch fire' and somehow the engineer named gordon was trying to reverse engineer a chip using an oschiloscope and writing down the voltage of every pin. from what i know 0 volts means logic 0 and +5 volts means logic 1. what does the -5 voltage that he was mentioned as a logic state? and also how was he able to write down a hex code just with a pair of leds connected to a bread board?