Specifications

4-11
MS-3207 Specifications
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 vast majority of standard RS-232 hosts over cable
distances of six feet or less, even under extreme conditions.
Multi-interface Miniscan Plus products fall into the TTL RS-232 device category right out of
the box. All standard RS-232 cables available from Symbol Technologies Inc. for the
Miniscan Plus family measure six feet or less, and should not present a problem. In the
event that a particular host does not support TTL levels, a separate conversion cable is
available. This cable (25-62186-xx) contains electronics to adapt the TTL levels of a multi-
interface Miniscan Plus 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. The
nature of USB is such that the root hub located on the host controls all traffic. All hosts are
not created equal and it has been found that 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 levels of Electro Static Discharge (ESD) or situations
in which the system is subject to Electrical Fast Transients (EFT).
Typical symptoms that these conditions exist are:
1. Frequent scanner resets
2. Scanner sometimes loses power (Occurs due to host initiated shutdown)
3. Occasional host lockups
Multi-interface Miniscan Plus products are often exposed to such environments due to the
nature of scanner placement, etc. As such all Miniscan Plus products have been
safeguarded as much as possible against these phenomenon and will not suffer physical
damage. Despite design precautions, testing has shown that some USB hosts cannot
tolerate these types of disturbances. In these situations a self-powered USB hub placed
close to the host, between the scanner and host, can sometimes serve as an effective
buffer to the host against the harsh environment the USB scanner lives in. This may not be
a valid solution in all cases.