Connectivity

Every embedded system ends up moving bytes between two chips that were not designed together. The bus chosen for that job decides more than throughput: it decides latency, determinism, cable length, connector cost, and how much of the protocol you have to implement yourself.

Choosing a bus

CAN was built for vehicles and kept for anything that needs short messages, arbitration without a master, and tolerance to electrical noise. It is slow by modern standards and that is not the point.

USB is the answer when a host is present and the peripheral must be recognised without configuration. Its descriptor model and class system carry most of the complexity, and most USB bugs are enumeration bugs, not transfer bugs.

PCI Express is the choice for bandwidth inside a board or a chassis. It is a switched, packet-based fabric rather than a bus, which is precisely why treating it like a bus produces designs that do not scale.

MIL-STD-1553B belongs to avionics and defence: dual redundant, deterministic, command-response, and unchanged since 1978 because that stability is the requirement.

HDMI carries video, audio and control on one connector, with the licensing and content-protection constraints that come with it.

What the courses cover

New digital buses (I0) is the overview for teams that have to choose rather than implement. CAN bus (IA1) and MIL-STD 1553B (IA3) cover the deterministic side, the one where a missed deadline is a failure rather than a slowdown.

PCI 3.0 (IC1) and PCI Express 3.0 (IC4) cover the high-bandwidth path, from configuration space to link training. USB 2.0 (IP2) and USB 3.0 (IP3) cover the host and device sides, descriptors, classes and enumeration. HDMI 1.4a (IM1) covers the display link.

Each course works from the specification and from a protocol analyser, because a bus is understood by watching real traffic rather than by reading about it.