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*
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
Hi Si,
In a word... Wow! I hadn't realised there was such a performance hit using JP
over JR!
A 24T JP is painful! I've always used JP - assuming (naively) that it was
faster based on
Z80 T-state lists.
So all these years I've been crippling my code with JPs when I should have used
JRs!
