Door Control Output - Recognition Systems HANDKEY II Manual

Planning an Installation
line in the RS-232 port from the host PC system. It should then be carried to one
of the ground terminals on the back of each unit in the network. An example of
this method of grounding is shown in Figure 2-4.
Connect the Cable
Shield to the
Master's Ground
Figure 2-4: Communication Shielding Carrying a Single Ground to Each Unit
If no earth ground is available at the units, this is the only possible method of
connecting the grounds. Even if an earth ground is available, depending on the
building's power wiring and other environmental issues, this method may be
superior to the previous one, since it establishes the ground of each unit
independently of the building power lines. Local variations in grounds between
buildings, or from one point to another in a very large building, (perhaps due to
elevator motors or other large-current drawing machines) will have no effect on
the communication network if this configuration is used.
However, the power supplies must be truly floating, with no hidden paths back
to the high-voltage side of the transformers, or to earth ground. Since this is
difficult to achieve (there is always some parasitic capacitance between the
primary and secondary in any transformer), this method may be more
susceptible to high-frequency transients in the high-voltage side of the power
lines than the earth-grounded method.
The master unit's ground establishes the ground for the entire system. The main
board ground points are connected to the shield ground at each unit, but are not
connected to earth ground. The ground point on the master can be the data
converter power supply negative terminal, or the GND pin on the RS-232 cable.
If the master is an HGU, its main board ground can be used. This configuration
should only be used if the power supplies to the units are truly floating,
otherwise ground loops will be created, and differences in local grounds may
cause large currents to flow through the cable shield.
Door Control The HandReader can operate a door in two different modes: lock output and card
Output reader emulation. The wiring for each mode is significantly different.
Page 14
Master
GND T+ T- GND
Connect Both Shields
to Remote 1 Ground
Remote 1 Remote 2
R+ R- GND
Connect Both Shields
to Remote 2 Ground
R+ R-
Connect Shield
to Next Remote
To Next
Remote