I am using P2.0 TO P2.4 as inputs. First four for 4 bcd digits from 7135, and the the next one for D5(digit 5) from 7135. (when D5 comes in, I start moving bcds in). 2.5 to 2.6 is used to switch 4051 which in turn selects the input to 7135 from 8 analog channels. Now,

1. When I write FF to port 2 and make it input port, I am able to read whole of p2 and write to p2 (I am using byte instructions only). My channels are switching, and I am able to sample 8 channels and read 7135 output.. I do have intermittent jumps in the readings, and I am yet to find out the reason. How does it work, since the port is supposed to be input-port? More over, I am using byte instuctions for outputting.

2.When I try to make p2 = 5 inputs and 3 outputs, the program hangs. I am outputting 8f in the initialisation stage itself.

3. If I mix the port pins as input/output, how do I output address lines at the same time? ie: If I set the pins one by one, there could be problems, if chip being addressed is already enabled.

4. Analogue switch output does not become zero when input is zero. Even if the input is very low, 7135 sems to be converting it (15 mv/count). The problem now, is that, since there are 8 channels, the error for each channel is slightly different. I am not able to use a common correction factor. How do I deal with this problem?