SIGNAL PROBE ON LOGICWORKS 5 SOFTWARE
While a variety of programming software is possible, among the most-used variant is ladder logic. In addition to scientific instrumentation, production facilities make use of RS-232 in PLCs, which are generally connected to and controlled by ruggedized laptop computers through Ethernet, RS-232, RS-485 or RS-422, all related technologies. And there is an RJ45 version (bottom) defined by EIA-561 for nonsynchronous apps only. Though the 25-pin D-shell (top) is the primary RS-232 connector style, some old PCs used a 9-pin version (center). But RS-232 remains the dominant data and clock bus on the harsh factory floor and in industrial locations world-wide, where the bulky, rugged connectors are actually a plus. It is easy to see why USB has replaced RS-232 as the predominant bus technology for data transfer between computers and peripherals as well as numerous similar applications in reasonably forgiving environments. This procedure presupposes, of course, that the system is wired correctly and that the pin outs correspond to the RS-232 standard. If the voltage on pin 3 is more negative than -3 V, you are looking at a DCE. If the voltage on pin 2 is more negative than -3 V, you are looking at a DTE. Be certain in all cases that the black multimeter lead is connected to pin 7, which is signal ground. Measure the voltage first between pins 2 and 7, and then between 3 and 7. The identity of any two units that are in communication can be ascertained by measuring the voltage on certain pins. Normally, a personal computer is DTE and the modem is DCE, regardless of which is transmitting at the moment. Throughout any discussion of the RS-232 bus, the distinction must be kept in mind between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE). Pins 15, 17 and 24 are used to convey a clock signal, which is used only for synchronous communication. Normally, these pins are on throughout the communication session. Pin 4, request-to-send, is a signal sent from the transmitter and pin 5, clear-to-send, is a signal sent from the receiver. Pin 2 transmits data and pin 3 receives data. Independent channels make possible full-duplex simultaneous communication between a central processing unit and its peripherals. RS-232 is a single-ended as opposed to differential bus.
SIGNAL PROBE ON LOGICWORKS 5 SERIAL
Moreover, with 25 pins at each end, cabling and terminations cost more, compromising an important rationale for the move from parallel to serial communication. Unlike USB, significant amounts of power could not be conveyed from host to peripherals. This involved a larger media inventory, not to mention the possibility of error. In an important respect, RS-232 resembled Ethernet in that to link identical computers or other devices, crossover cables were needed to matchup transmit and receive pins. Multiple drops to three and more devices required improvisation, placing upper limits on speed and hampering compatibility. Also, noise immunity and transmission distance were compromised because of single-ended signaling referenced to a common signal ground. Because of the voltage swing, maximum speed was limited. One problem with the earlier design was that use of large voltage swings and the need for both positive and negative supplies resulted in excessive power consumption. The original RS-232 was less ambitious than more recent electronic bus protocols. However, a degree of confusion ensued because of proliferating peripheral devices that varied somewhat in electrical requirements, notably their use of reduced voltage levels. Early terminals were built so as to be compatible with teletypewriting equipment. At first it was envisioned to apply to teletype machinery with associated modems. RS-232 was introduced in 1962 as an EIA Recommended Standard. A 25-pin D-sub connector for RS-232 bus connections and its pin definitions. Circuit functions were described in the manner of similar standards. The standard furthermore defined interface and connector construction and pin outs. It was thoroughly codified by the Electronic Industries Association in RS-232-C (1969) with regard to electrical signal qualities including voltage levels, signaling and slew rate, timing, voltage-withstand level, and short-circuit and load capacitance metrics. Unlike SPI, RS-232 was not a mere de facto standard. This despite some downsides: low transmission speed, large voltage swings, and bulky connectors. It is still widely used in programmable logic controllers (PLCs), networking equipment, and scientific instrumentation. This old protocol seems rather clunky today alongside sleek new USB schemes with their many user benefits. The trapezoid-shaped 25-pin array inside the rectangular connector was a familiar sight a few years back, in an age when computers were connected primarily by means of the RS-232 bus.