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7820A GC Installation Manual
The bus is passively pulled high. Leakage current out of a
port must be less than 0.2 milliamps to keep the voltage
from being pulled lower than 2.2 volts. Higher leakage
current may cause the state to be interpreted as a low.
Over-voltage protection - APG Remote connections are
clamped by a zener diode to 5.6 Volts. Exceeding this
voltage will damage the circuit (main board).
APG Remote - Suggested drive circuits A signal on the
APG bus may be driven by another APG device or by one
of the following circuits:
• A relay, with one side connected to ground, when
closed will set a logic-low state.
• An NPN transistor, with the emitter connected to
ground and the collector connected to the signal line
will set a logic-low state if proper base current is
supplied.
• An open-collector logic gate will perform this same
function.
• A low-side drive IC will also work, but Darlington-type
drivers should be avoided as they will not meet the
low-side voltage requirement of less than 0.4V
APG Remote connector
Figure 13
shows the pin-out details of the APG Remote
connector.
7820A GC Installation Guide
35
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