Hi Chris, The short answer is Yes, it's best to use JR e over JP nn on SAM.
In the best-case border area, both are 12T. Fully on the main screen, JR is typically 16T and JP is a whopping 24T. It does depend a little on the starting cycle alignment, and instructions spanning the screen edges are more complicated to work out. In general, shorter instructions mean fewer memory reads, and less memory contention. JP (HL) is as fast as a NOP, at just 4T in the border and 8T on main screen. Si Chris Pile wrote: > Just a quick question regarding memory contention on the SAM and its > effect on JP and the > *unconditional* JR instruction. > > Z80 timing lists state that JP takes 10 T-States whereas an > *unconditional* JR takes some > 12 T-States. However, does the SAM's memory contention make all > *unconditional* JRs > faster (or as fast) as the JP due to the JP needing another memory access? > > Just a simple "Yes, always use JR over JP in unconditional cases" - or - > "No, stick with JP > as it's faster!" please guys, as my head explodes reading too much > hardware-based theory! > > Cheers... > Chris.
