S-100 Bus - Architecture

Architecture

The S-100 bus essentially consisted of the pins of the Intel 8080 run out onto the backplane to form the single system bus. One early, unanticipated shortcoming was various power lines of differing voltages being located next to each other, resulting in easy shorting. This was addressed in later systems. The system included two unidirectional 8-bit data buses, but only a single bidirectional 16-bit address bus. Power supplies on the bus were unregulated +8 V and ±18 V, designed to be regulated on the cards to +5 V (used by TTL) and ±12 V (typically used on RS-232 lines or disk drive motors). The onboard voltage regulation was typically performed by devices of the 78xx family (for example, a 7805 device to produce +5 volts). These were linear regulators which, depending on the current load, could produce a good deal of heat.