Microcntroller 89c51 input through keypad.

Hi Guys,
I am trying to build an 89c51 based project wherein i have to create a matrix of 24 keys . And the wire length would be very long .Hence I used uln2803 as a buffer .I tried the code amd hardware using Pic18F4520 it worked fine .
I used interrupt on change feature .
Now I am trying the same code with 89c51 IC , hence I have to use generic input keys instead since it dows not have interrupt on change , but when i simulate the same in proteus only two ports work the third one does not work . I have attached the proteus file that would give a better idea . I suspect its some thing to do with proteus .I hawent tried the hardware on general purpose pcb , but for pic18f4520 it worked .

For 18F IC I connected the LATC as output to the input of ULN IC ans then connected the output of uln ic to LATB.B5 B6 and B7 iocb pins through buttons , which were pulled up through 10 k resistor .
Initially when i run th esimulation the button one end is low and another is high on pressing the button they go low .
But when using 89c51 only two x 8 series work the third 1 x 8 keys do not work at all .

Please help .

Thanks & Regards .