Product specifications

COMMUNICATIONS
Sharp Electronics Corporation
More on Cabling
Cabling considerations - you should use cabling made for RS-232 data communications
using a high quality low capacitance data grade cable. The standard maxim length is 50'
but if data is Async you can increase that distance with a good grade of cable.
The RS-232 signal on a single cable is impossible to screen effectively for noise. By
screening (or shielding) the entire cable you can reduce the influence of outside noise, but
internally generated noise remains a problem. As the baud rate and line length increase,
the effect of capacitance between the different lines introduces serious cross talk (this
especially true on synchronous data - because of the clock lines) until a point is reached
where the data itself is unreadable. Using low capacitance cable and shielding each pair
can reduce Signal Cross talk.
The maximum distance will depend on the speed and noise level around the cable run.
On longer runs a line driver may be required. This is a simple modem used to increase the
maximum distance you can run RS-232 data.
Cabling Construction
Beyond the obvious traits such as number of conductors and wire gauge, cable
specifications include a handful of less intuitive terms.
Characteristic Impedance (Ohms): A value based on the inherent conductance, resistance,
capacitance and inductance of a cable that represents the impedance of an infinitely long
cable. When the cable is out to any length and terminated with this Characteristic
Impedance, measurements of the cable will be identical to values obtained from the infinite
length cable. That is to say that the termination of the cable with this impedance gives the
cable the appearance of being infinite length, allowing no reflections of the transmitted
signal. If termination is required in a system, the termination impedance value should match
the Characteristic Impedance of the cable.
Basic constructions
Wire and cable consists, for the most part, of four basic constructions:
• Single conductor
o One conductor, bare or insulated.
• Multi conductor
o Multiple insulated wires
• Twisted pairs
o Two insulated wires usually twisted together
• Coaxial cable
o Insulated center conductor with a shield and jacket overall.
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