Alarm interface circuit

Alarm interface circuit . As shown in the figure, a two-color light-emitting diode is used for display. When LAi is high level
and LBi is low level , the LED displays green; conversely, when LAi is low level + LBi is high level, the LED displays
red; if both are high level , the LED displays red yellow. Each LED in the system indicates an annealing furnace. It displays green when the temperature is normal,
red when it is higher than the upper limit, and yellow when it is lower than the drop value. In this way, the operator can know whether each annealing furnace is working normally based on the display color of the two-color light-emitting diodes at any time. The control of the display color is completed
by the C port ( PC O ~ PC 7) of 8255A and the Pl port (P17 ~ Pl0) of 8031 ​​respectively.