My Bad, as they say. I am familiar with the "access bank", and with the paging register on earlier chips. I have read the data sheets (not every page) but was confused by the statement in the app note an upgrading to the 18Fxxx architecture, which said that RAM/register addresses should be written to specify 3 digits, as in "0x087" - which could take one all the way to 4096 bytes of RAM. Combine that with information which placed the "access bank" in the upper half of Page15, and I made the jump to thinking the RAM space was flat, not segmented. Oh well, too bad. As I said, I can't understand why they fixed almost all of the other addressing oddities and left the Page Register in there. Its kind of nice for context switching, but since I don't need to do that very often, a flat memory space would have been more to my liking. If I am writing code which needs serious context switching abilities I will be using a "C" or Basic compiler anyway, and the ones I know of take care of those details in the background. Roy J. Gromlich ----- Original Message ----- From: "Olin Lathrop" To: Sent: Wednesday, January 14, 2004 6:02 PM Subject: Re: [PIC]: I hope I am missing something here > Roy J. Gromlich wrote: > > I will have to take a look at the paging issue - I am totally > > surprised that they have a 12-bit address for the RAM but still need > > a page register. > > This is why it's best to read the manual *before* programming the chip, duh! > > Anyway, the 18 family does have a 12 bit address space for data memory. > However, most instructions only encode 8 bits of this address. The upper 4 > bits have to come from somewhere, which in this case is the BSR register. > Some instructions, like MOVFF, do encode all 12 bits. But, note that MOVFF > takes two program memory locations and two cycles. > > Then there is the "access bank", but I don't want to spoil your reading by > giving away the whole plot up front. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.