In the 7447 BCD to 7-segment decoder chip, pin 4 is BI'/RBO'. That pin acts both as input and output. I would like to understand how exactly the internal circuitry works to make this possible. On page 7 of this datasheet, there is a schematic showing the internal circuitry for the BI'/RBO' connection. Can somebody please explain how exactly this works?
Does the dashed line on the right carry the pin signal fed to the rest of the chip circuitry? If so, how can the signal there ever attain the logical "high" state? The two diodes in series will always clamp down the voltage there to be the sum of two diode forward voltages (i.e., max ~1.4V total).