[cesarb]

> Firmware is software. [...] but I'm having trouble imagining how some TV could possibly be damaged by software.

It's not very hard to imagine. For instance, most embedded chips have several "general purpose" I/O (GPIO) pins, which can be configured as an input or as an output; their usage depends on how the chip was wired into the circuit, and very often, they're shared with "alternate functions" like a serial bus. Configure them incorrectly (as an output when they should be an input, for instance), and you can easily create a short circuit, burning that pin or even the whole chip.

[Dylan16807]

Is that particular risk common? I would generally hope that I/O pins put out few enough milliwatts that they can be shorted safely.

[HALtheWise]

Yep! Most microcontrollers will sustain permanent damage if you short an output pin for any significant time. You could probably design a microcontroller that didn't do this, but it would require putting a big resistor in line with the pin (decreasing responsiveness and max power output) and/or adding a lot of circuitry and increased cost to defend against a risk that's not a big deal when the chip is being programmed by a competent embedded engineering team.

[Dylan16807]

A lot of circuitry? I would have thought a handful of (integrated) transistors could make it happen.

[wtallis]

Transistors that can handle a lot of current or voltage will need to be much larger than most of the logic transistors on a chip, so even though they may appear to be few in number on the schematic, they can add up to significant die area for a small part like a microcontroller.

[Dylan16807]

They need to control the transistor that actually does the output, so they shouldn't need to be very big themselves.

[nunuvit]

This is a layer below the digital circuit abstraction in the territory of analog circuits and device physics.

The extra current is a physical thing and you need more material to temporarily withstand it, and more circuit to detect and control it. Since it's an uncontrolled switching event, it'll probably ring unless you add even more components to absorb and control that. Then that could exceed the physical limits and trigger a parasitic circuit that doesn't have an off switch, so you need yet another circuit to detect and shut it off somewhere else.

It can be a lot of work for the board designer to make it reliable and compatible, assuming the other chip it's talking to can also handle the extra current. It's cheaper and more reliable to type GPIO1DIR=OUT or whatever. Sort of like when you drive a car, it's easier to choose to drive in the correct lane than it is for the car to enforce it on you and protect you if you do it anyway.