Making effective use of serial devices often involves converting between RS232, RS485, and USB signals. Compatible with TTL/RS485 standard, converting the TTL signal into a balanced differential RS485 signal, supporting full-duplex communication. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. The RS-485 standard calls for a differential signaling scheme that will operate over a much longer line length than RS-232 can. Adding a low-pass RC (Resistor-Capacitor) filter to each input line is easy with SMINI. The SMINI card is designed so that each input line is wired from the external hardware directly into the appropriate pin on input buffers U3-U5. Thus, if you are not currently interested in implementing input line filtering, simply skip ahead to SMINI Parts. Adding a resistor to the end of the cable that matches the value of the cable’s impedance will absorb the signal traveling down the line and reduce or prevent reflection.
The performance of the cable should work for the application. In place of using hardware filtering, you can perform software filtering in your application program. This is extremely heavy filtering and probably more than needed for even the most severe situations. For example, if your requirement does not demand a fast response time for reading inputs, and you desire heavy filtering, I would suggest using the 100Ω resistor with the 10 or 22µF capacitor. Larger capacitors make these high-level currents present for longer time-periods exacerbating the drive requirement. The 2N4403 PNP transistor provides a drive capability of .3A. The following table provides an overview of the two standards. Onboard unibody power supply isolation, provides stable isolated voltage and needs no extra power supply for the isolated terminal. The software simply checks to see that the input has remained stable for two or more samplings before it accepts any change in input. We also see that the maximum allowed voltage levels for all interfaces are in the same range, but that the signal level is lower for the faster interfaces.
Receiver Input Sensitivity: RS-485 has a receiver input sensitivity of ±200mV, which means a receiver must see signals above or below 200mV to recognize a mark. When configuring an IBM PC’s serial port, the parity, number of data bits, and number of stop bits must be set; therefore, many think this must be part of the RS-232 standard. This protocol may include things like the start bit, number of data bits, parity and stop bit(s). The difference in earth ground potentials between these two computers may be tens or even hundreds of volts. In this case the desired maximum capacitor value would be about .02µF, which is quite a difference. Devices using the RS232 protocol are limited to a distance of 15 meters between transmitter and receiver while still achieving the maximum data transmission rate. Variably, this time both TX and RX have their own 2 wires for data transmission.
All Series 970B transducers have an analog pressure output of 0.5VDC/decade that can be interfaced to external analog equipment for pressure readout or control. The Series 970B have standard 15 pin HD Sub-D connector. RS-422 does not specify any connector. RS-422 is full duplex so it can use the X-On / X-Off protocol, if needed. Could you use some assistance? Also, for applications where you desire to filter out high frequency noise, it is better to use tantalum, disk ceramic or monolithic capacitors in place of the frequently lower-priced electrolytic capacitors, which are less effective at the higher frequencies. It is my personal experience that few applications require input line filtering. The emulation feature can be used to upgrade and replace other vendors’ gauges in OEM applications without changing system software. In the central chemical dosing and dispensing system of China’s Hingsen Semiconductor, the configuration comprises central chemical storage tanks coupled with dispensing systems at each process point, controlled through valve boxes to regulate the supply of chemical reagents. 5V TTL signal level, with anti-reverse connection and anti-over-voltage circuit on the power supply side.
