Digital serial interfaces

The ICs discussed in this chapter will be strictly the D/A and A/D conversion circuits. The ICs usually perform either D/A or A/D conversion. There are serial interface ICs, however, typically for digital signal processing applications, that perform both A/D and D/A processes. 

Input/output ports Timers and counters Interrupt controls Analog to digital converters Digital analog converters Serial interfacing ports Oscillatory circuits... 

A dedicated microcomputer is interfaced to the Instron instrument in order to collect the raw data. The microcomputer consists of an 8080A microprocessor, 32K bytes of memory, A/D converter, serial I/O for communication, parallel I/O for digital control and sensing, a real-time programmable clock, and vectored interrupt control. 

The A/D board can reside either in the detector, an interface box, or in the computer. If the board is in the computer, it will have analog input terminals similar to a strip chart recorder or it will be connected to an interface box that will have this type of connector. If the A/D card is in the detector, the detector will have some type of digital interface port and a cable to connect it to the computer. In the personal computer world, once the signal is digitized outside the computer, it will be sent to the computer over one of three types of communication cables parallel, serial, or GPIB. 

RS232 serial port or IEEE488 interface bus). The plug-in cards use the computer power supply which tends to contain noise generated by all of the digital pulses generated in the computer. Higher bit conversion would not introduce improved measurement accuracy because of this noise. 

Modern multimeters maybe equipped with memory possibilities, and/or interfaces to a personal computer by infrared, IrDA, or serial link, RS-232, or an instrument bus such as IEEE. Modern portable DMMs may have accuracies as good as 0.025%, whereas nowadays bench-top instruments reach accuracies in the single-digit parts per million figures. 

Phase 3 Digital To Host. A/D conversion moves into the laboratory device and BCD or ASCII digits are sent in serial or parallel to the host. The laboratory device now looks like a terminal. The controller operates in character interrupt mode. Logical extensions of this technology have followed the manner in which we interface terminals. The first interface is a single card interfaces and then multiple interfaces per card. However, both are interrupt driven and considerably load the CPU. The next logical step is a DMA or silo controller. There are "standards the RS-232-C (in many variations) and the IEEE-488. 

RS-232-C In asynchronous transmissions, a recommended standard interface established by the Electrical Industries Association. The standard defines the specific lines, timing, and signal characteristics used between the computer and the peripheral device and uses a 25-pin or 9-pin DB connector. RS-232-C is used for serial communications between a computer and a peripheral such as a printer, modem, digitizing tablet, or mouse. 

Fig. 3. Sketch of the hardware and software system used in the author s laboratory to investigate the electrode kinetics of electrochemical reactions. D.A.C are digital-to-analogue convertors, F.R.A. is a frequency response analyser, A.D.C. are analogue-to-digital convertors (used to switch devices), D.P.M is a panel meter, and NTWK is the university network serial connection to an Amdahl computer. The units I are the appropriate interfaces.

Interfaces to the PC world via the NERVIA netwoik. SPINLINE 3 may also interfaee with other analogy or digital systems using networks, serial data links or wire-to-wire links. 

A/D conversion, and the decoder portion of the codec performs the D/A conversion. The digital code is usually formatted as a serial data stream for ease of interfacing to digital transmission and multiplexing systems. 

An effective alternative is to constmct instruments with a built-in interface. The Ibercomp RS485 series of boards can be very useful for this purpose [72]. This series includes A/D converter, D/A converter and digital I/O boards that can be mounted on instmments and connected to a single RS485/ RS232C interface. The RS485 portion of the interface can support several boards and the RS232C portion ensures compatibility with computer serial ports. 

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