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MS XX07 Series Integration Guide
Application Notes
TTL RS-232
Standard RS-232 voltage levels typically range between +12V and -12V to ensure
adequate noise rejection over long distances. Devices which support TTL level RS-232
signaling typically drive signals between 0V and +5V. Extensive testing has shown that TTL
levels are interpreted correctly by the majority of standard RS-232 hosts over cable
distances of six feet or less, even in extreme conditions.
Multi-interface Miniscan products fall into the TTL RS-232 device category. All standard
RS-232 cables available from Symbol for the Miniscan family measure six feet or less, and
should not present a problem. If a particular host does not support TTL levels, a separate
conversion cable is available (25-62186-xx) which contains electronics to adapt the TTL
levels of a multi-interface Miniscan into standard RS-232 levels.
USB Warning - Potential Host Side Issues
The Universal Serial Bus provides a smart plug-and-play interface for easy integration. In
USB communication, the root hub located on the host controls all traffic. USB hosts in
general react poorly in certain harsh environments compared to traditional host interfaces
such as RS-232. These environments include areas with high ESD levels or situations in
which the system is subject to Electrical Fast Transients (EFT).
Typical symptoms of these environments are:
•
Frequent scanner resets
•
Scanner occasionally loses power (due to host initiated shutdown)
•
Occasional host lockups.
Because multi-interface Miniscan products are often exposed to these environments due
to the nature of scanner placement, they have been safeguarded as much as possible to
prevent physical damage. Despite design precautions, testing has shown that some USB
hosts cannot tolerate these environments. In this case, try placing a self-powered USB hub
close to the host, between the scanner and host, as a buffer to the host against the harsh
environment. This may not be a valid solution in all cases.
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