Comtech EF Data RC-1160 - Manual (Page 65)

Theory of Operation Revision 1
RC-1160 RC-1260 Redundancy Switch Controllers MN-RC1160RC1260
C-5
Bus driver chip U22 buffers the microprocessor outputs to the waveguide switch driver PWB. The bus driver
chip supplies the necessary current to activate the opto-isolator switches. Time constant C18 and R73 form a
power-up delay holding U22 outputs in a tri-state position. This action prevents indeterminate states of the
microprocessor from pulsing the waveguide switch commands until after the switch controller is initialized.
Lamp test is initiated from the front panel in the Local mode by depressing the push-button, supplying a ground
to the logic board on P14 pin-2. This pulls the diode clamp line low on pin-9 of U15, U19, and U20. the output
relays are activated directly from the microprocessor through the drivers U17 and U18 to the relay coils. The
inductive spikes produced by the de-energizing of the coils is forward conducted from their pin-9’s to the +13V
supply.