Does anybody know the maximum current that these diodes will carry as they
dont appear to be detailed in the book (16c55)

signal------100k------port pin

this is repeated on all of port b and port A0-2 the driving signal is -12v to
+12v and thus gives a current into each pin of 120ua on negitive going signals
and 70 ua on positive going signals worst case total of 1.3mA negitive or
770ua on positive going signals the power supply for the chip is a TL431 shunt
regulator so voltage increase is not at issue here.