C1 + M1
C1 and M1 devices are interconnected by four interface lines:
As was explained, C1 devices do not have dedicated ground and power lines.
Sometimes, such lines are just not necessary. For example, Tibbit #27 (IR receiver/transmitter) works fine without the ground and power:
Some C1 devices, such as #18 (power input) do need to be connected to the system ground. Tibbit #18 was designed to be used with power supply Tibbits #09 and #10. These "M" devices provide ground on their pin 5, and this solves the problem. Incoming supply voltage (Vin) is routed through pin 1:
Several C1 Tibbits implement various sensors: temperature, humidity, pressure, etc. These need both the ground and +5V power lines, which are provided by the "M" Tibbit #00-3. This Tibbit propagates ground through pin 5 and outputs +5V power through pin 4: