Digital Signals

DIGITAL SIGNALS:

In a computer, all data must be reduced to an electrical switch.A switch has only 2 possible states, “on”and “off”, so it has only 2 numerical symbols, 1 (on) and 0 (off). Because there are only 2 symbols it is known as “Binary”.

Each 1 and each 0 is known as a “bit”, 8 bits together is known as a “Byte”or a word. Computers can store thousands of bytes of data, the only limit is the size of the memory. For example, the MEFI 4 can store up to 2 thousand bytes (2K) ofcalibration data, where as the MEFI 1 can only handle 512. This means the engine parameterscan be monitored and adjusted in finer increments, such as 50 RPM instead of 200 RPM.

Digital Binary is used by computers to communicate with one another and within itself. To a computer 10011101 might mean “turn on the fuel pump”.

Examples of digital inputs to the ECM are MEFI 4 CKP and CMP signals, Ref Hi input for MEFI 1 and MEFI 3 engines, the oil pressure switch and the exhaust riser temperature switches. The switches tell the ECM about a switch open or closed status. The CKP, CMP and Ref Hi inputs form a repeating high/low pattern that the ECMinterprets as crankshaft speed and piston location.