Hi All,
And Merry Xmas.
Consider an 8255 to be put on addresses 0000H through 0003H on an 8051 with the rest of the address space allocated to a 28F512 flash, i.e. no address "alias"s for the 8255. In order to decode the address lines A2..A15 to deliver appropriate ChipSelect signal to the 8255 and 28F512, What do you sujjest except for using GALs? I could not figure out anything but five 74HC138s with A2 through A15 connected to their input pins. I just cant't "write" my schematic here, but I'm sure those of you who may be interested manage to figure out that decoder. It probabely works, but the propagation delay with this decoder seems to bother me and the number of 74138s seems to be somewhat more than it should be.
Best.