6K V1.02 03-16-91
22
12.
LOGIC OUTPUTS
Your 6K controller has the ability to control "logical" devices at the repeater site. "Logical" devices
are relays, lamps, solenoids, IC logic, and other devices that are turned ON and OFF.
The controller has three logic outputs dedicated to this purpose.
Logic output #1 is pin 7 of J2. Logic output #2 is pin 8 of J2. Logic output #3 is pin 9 of J2.
Each logic output has a hardware interface circuit that is designed exactly like the TX PTT output,
except that the power MOSFET is smaller. You may wish to refer back to the "TRANSMITTER
PTT" section of this manual for a discussion of the hardware design of the output circuits.
The power MOSFETs used as logic output drivers appear as 5-ohm resistances to ground when in
the conducting state (ON). When ON, they can sink up to 75 mA. The MOSFETs appear open
when in the non-conducting state (OFF). When OFF, they can withstand 40 V DC. Do not control
loads over 40 V DC, since the transient protectors across the MOSFETs will start drawing current
as the voltage increases beyond this limit.
Since the drain connections of the MOSFETs are brought out to the connector without "pullup"
resistors, this configuration is called "open drain". This is similar to the "open collector" configuration
used with bipolar transistors. An ohmmeter cannot be used to check the logic outputs, since no
change will be seen when the outputs are switched between ON and OFF. A DC power source
and a load of some type are needed to see the outputs change state.
Logic outputs are very handy for controlling external devices and appliances at the site. Examples
of loads include lamps, LEDs, relays and other devices that operate from higher voltages (up to 40
V DC). If the loads are integrated or discrete logic devices that operate from 5 V, you can make the
logic outputs compatible by connecting pullup resistors of 3k ohms from the outputs to the 5 V
power supply of the devices being driven. Other types of logic may require pullup resistors to +10 V
or +12 V. Note that although the power MOSFETs are protected by transient suppressors in the
controller, it is still important to wire diodes across inductive loads (such as relay coils and solenoid
coils) in the non-conducting direction.
Each logic output can be latched ON or latched OFF. Each can also be momentarily turned ON or
OFF. There is no need for sense-reversal dipswitches on the three logic outputs.
The controller will remember the state of each logic output during power outages. When power
returns, the controller will turn each output ON or OFF to match its condition before the power loss.
A "cold start" (initialization) will force all output OFF.
