DPP Card Replacement Guide BCS35 and up
103
Power and alarm communications
circuit pack
The Power and alarm communications ( P/A Comm) circuit pack, located at
the rear of the A chassis in position 16, performs a multipurpose function. It
provides communications between the Quad SIO circuit pack and various
peripherals. Its circuitry responds to switching signals from the error control
II circuit pack or keyboard–entered commands. Furthermore, it provides
power detection, alarm generation, and ac clock circuitry.
The P/A Comm circuitry detects the loss of output voltages from the DPP
power supplies. Six optoisolators are connected in a series string, insuring
that any voltage loss interrupts the string and deenergizes the power alarm
relay (K7). This causes a form C relay to change state, signalling an alarm
condition.
This circuitry also provides operating power for the circuit pack. The +12 V
dc, –12 V dc, +8 V dc, and +5 V dc supplies are all monitored and
connected to guarantee power to the circuit pack as long as at least DPP
power supply is operational. The +8 V dc passes through a regulator to
p5 V dc power for the logic circuits.
The P/A Comm circuitry also generates external alarms using signals from
the error control II circuit pack. Three relays on this pack signal alarm
conditions to devices outside the DPP. The circuits which drive these relays
are also on the circuit pack. The three relays follow:
•
K1 – Minor Alarm
•
K2 – Major Alarm
•
K3 – Critical Alarm
The ac clock circuit generates timing pulses from a 19 V ac, 60 Hz external
source, if equipped. Two such circuits can be provided, one for each DPP
chassis. In the circuit, a 60 Hz input is fed to an ac optocoupler to prevent
ground noise. The optocoupler produces a 120 Hz signal, divided by two to
produce a 60 Hz signal. This signal drives a transistor, providing extra drive
capability for sending to the CTC on the CPU circuit pack.