lets make a subroutine that can set or clear a selected bit in the CTC control register.\u00a0 To call the routine, we need to tell it:
\n– The CTC channel
\n– Which bit we’re adjusting
\n– If we’re setting or clearing the bit<\/p>\n
Lets put the CTC channel’s port on the B register, the bit we’re adjusting in the C register, and…. do we use a register or a flag for setting or changing?\u00a0\u00a0 Lets use the zero flag and see what trouble that gets us into.<\/p>\n
Oh snap, there’s bit setting instructions, and they work with any register!\u00a0 set n,A would set the n’th bit.\u00a0 Can the n be derived from the value of a register?\u00a0 Lets assume not.<\/p>\n
Actually, before we do any of that, lets see if we can get relative jumps working correctly.\u00a0 Maybe we can get the number of jumps from the B register, and have a series of SET instructions<\/p>\n
Using JR 01, I’m getting a compiler error “Byte out of range”.\u00a0 When I look at the listing, I see the offset listed as EE, which doesn’t make sense… AH – The assembler automatically subtracts 2 to make up for the fact that the PC has already incremented by 2! So when I was trying 1 or 2, it would fail!\u00a0 OK, but 4 fails too…<\/p>\n
There’s something about how this assembler handles JR that I don’t understand.
\nOK – it looks like you can only use JR with a label in assembler.\u00a0 Oh wait,\u00a0 you can’t do what I was originally thinking – you can’t get the offset of a Jump from a register??<\/p>\n
From Cowlark.com<\/a> : WHAAAA?!\u00a0 FUUUUUU…..<\/p>\n OK, well THAT’S Stupid.\u00a0 Damn.\u00a0 I thought even the lowly 6802 did that…<\/p>\n so can we What if you… lets make a subroutine that can set or clear a selected bit in the CTC control register.\u00a0 To call the routine, we need to tell it: – The CTC channel – Which bit we’re adjusting – If we’re setting or … Continue reading
\n“There is no variable indexing (like the 6502’s LDA <\/code>(ptr), <\/code>Y<\/code> addressing mode) at all. The index registers support a constant -128..127 displacement only.”<\/p>\n
\n1 – modify the operand byte after the JR Instruction?
\n2 – use one of the index registers? Does this mean 16 bit addition?<\/p>\n
\n1 – jumped to a routine
\n2 – set IX to the next address
\n3 – add C\u00a0 to the IX
\n4 – JP(IX)<\/p>\n","protected":false},"excerpt":{"rendered":"