Hi all I have interfaced 64K SRAM and 8255 PPI to 8051RD2 for scanning Matrix keyboard. On resetting the system all port pins of 8255 go to high impedence state. i am using Memory map technique to access 8255 resources.Latch and decoders are used to enable them. Port A:0x8000 Port B:0x8001 Port C:0x8002 Port CW:0x8003 required PCL = o/p PCH = i/p,PortA=PortB=i/p on Power reset 8255 is given 0x9B from 8051 while 8255 is accessed SRAM is disabled. After codes are executed nothing seems to happen.8255 is enabled while it is reffered by using above address. How can i go forward to make this ckt working ? ie atleast first to set-reset port pins. for proper 8255 reset i have tried two ckts a)reset signal of 8051 was given to NPN transistor to invert it. b)resistor capacitor combination,where res(10K)-->VCC,capacitor(10uf)-->gnd ckt response was same with both. where things might be going wrong ? while i was manually connecting PC.0 pin to gnd,All other pins of PC turned to same voltage,even when they are not shorted to each other. Should i give pull up to port Pins ? Regards Naresh