The serial data transmission mode finds its greatest use in multiple detector/converter systems where data must be sent over moderate distances to long distances to the computer. The system is easy to implement, has good noise immunity, and is reliable. The main disadvantage to the serial system is its moderate speed of transmission, which, for the older operating chromatographs was about 3000 bytes/sec when manufactured. Transfer speed, however, with the introduction of modern high speed solid state devices have greatly increased and today transfer speed is not a problem.

In parallel transmission the outputs of the counter are connected directly to a peripheral interface adapter (PIA) and thence to the data bus of the computer. The computer data bus is a parallel system of conductors by which the binary data is transferred between the central processor, memory and peripheral circuits. As the data bus is used for all data transfer, and each transfer involves different data levels, the data bus can not be continuously connected to the register of the A/D output.

Figure 37 The Function of the And-Gates in the PIA