First of all, in the sample code, F8 is a mask for the carry, digit carry, and zero bits. This sample will clear those 3 bits only. To access page 1 file registers, simply use this: bsf STATUS,RP0 mov** file To switch back to page 0 file registers, just clear the bit. It's that simple!!! for the "h" (hex), I think it's just expressing the same number in 2 different formats. Example: h'A4' = 0xA4. As for the crystal, there's an internal /4 from crystal speed to actual processor speed ---------- > From: Fernando Scalini > To: PICLIST@MITVMA.MIT.EDU > Subject: memory terminology > Date: Wednesday, November 26, 1997 12:19 AM > > Excuse my ignorance of such basic knowledge, but 3 books and several weeks of > banging my head against my desk have driven me to this. > > I can't figure out how memory is mapped for the PICs (16c84). the data > sheets show bank 0 from 00h to 7Fh and bank 1 from 80h to FFh. I think I've > finally figured out the concept of data banks and register shadowing but > their is a sample program in Predko's book that clears the STATUS flags as > follows: > > movlw 0x0F8 > andwf STATUS > > What does the "h" in the memory maps mean, and where does the final 8 in > 0x0F8 fit in to this format. Also, 0x0F8 was never defined previously in the > program. why was this address selected and how can you know what its value > is. > > Another quick one: If a processor is rated at 4Mhz, why use only a 1Mhz > crystal. > > thanks for your help.