Scott Dattalo says:
The ambiguities were:
1) Do the rotate instructions really affect the Z bit? Yes they do. This is different than the 12 and 14 bit cores. So be careful when you port your c74 code over.
2) What happens if an indirect register is the object of indirect? For example:lfsr indf0,0 ;Load fsr0 with the address of indf0 movf indf0,w ;double indirection? Nah..
Like the 14-bit core, this will load W with zero regardless where indf is pointing. This is not too unexpected. But what about this:lfsr indf1,0 ;load fsr0 with the address of indf1 lfsr indf0,2 ;load fsr2 with the address of indf0 movff preinc0,postinc2 ;?
As I understand it, the first fetch will read zero because fsr0 is pointing to an indirect register (indf1). This zero is then written to the address that is contained fsr2. However, fsr2 points to an indirect register (indf0). Consequently the write is ignored.
3) I also had a question about whether the program memory addresses were always even. The answer is yes - even though all instructions are 16 bits wide. The reason is that the table reads and writes to program memory can occur on byte boundaries. Now if you look at the instruction set closely you'll notice that the least significant bit of the program counter is never used EXCEPT for the table reads and writes. Examine the offsets for the branch instructions for example.
|file: /Techref/microchip/18diff.htm, 1KB, , updated: 2003/5/14 14:25, local time: 2016/12/10 14:37,
|©2016 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/18diff.htm"> microchip 18diff</A>
|Did you find what you needed?|
PICList 2016 contributors:
o List host: MIT, Site host massmind.org, Top posters @20161210 RussellMc, Neil, IVP, alan.b.pearce, James Cameron, Denny Esterline, John Gardner, Harold Hallikainen, Van Horn, David, David C Brown,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!