You can make out most of the markings, showing 1N4148 on the diodes. There as input protection, clamping the voltages on the input to the 5V rail after they pass through RP5, which looks like a SIL resistor array, probably something in the range of 1k to 4k7. Then C5 to C8 provide some EMI filtering and low pass with the resistors, and the diodes clamp the voltage to the positive rail. The resistor array above the diodes likely is a commoned block, providing a 22k to 100k pull up for the inputs, so the switches pull them to ground to activate the input.