Ok, i haven't read all the posts on this, but why not stick the code in LMPR and use IM1 - saves having the table of vectors.
Adrian ** UIP Sam Port 4100+ lines of z80 and climbing -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of David Brant Sent: 21 May 2008 06:46 To: [email protected] Subject: Re: Short, short questions I thought the idea of mode2 was you could have different vectors for different devices connected well this throws a spanner in the works. But then again is there any hardware for the SAM that uses them? I think it must have been an old spectrum book that said this about swapping high,low bytes. After a little test and using old brain this is wrong. Dave ----- Original Message ----- From: "Edwin Blink" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Wednesday, May 21, 2008 5:34 AM Subject: Re: Short, short questions > All 8 bits are used for LSB of the vector. The part where bit 0 always is > zero is when one of the Z80's IO chips is connected (PIO,SIO,CTC etc) is > connected. > > Edwin > > ----- Original Message ----- > From: "David Brant" <[EMAIL PROTECTED]> > To: <[email protected]> > Sent: Wednesday, May 21, 2008 1:02 AM > Subject: Re: Short, short questions > > >> I've just been looking at my books. Although I can't find the bit that >> said about swapping to high,low but I'm sure that I did read it >> somewhere. It does say that the device only gives the bits 1-7 and bit 0 >> is always 0 giving 128 possible addresses. >> >> Dave >> >> ----- Original Message ----- >> From: "David Brant" <[EMAIL PROTECTED]> >> To: <[email protected]> >> Sent: Tuesday, May 20, 2008 10:49 PM >> Subject: Re: Short, short questions >> >> >>> This was based on info from a book called z-80 Workshop manual by E.A >>> Parr. The I register gives the high part of the table and the hardware >>> gives the low part to the table then takes that word for the service >>> routine. So if you start from one byte before the table and use the same >>> address for all entries and over run it by one it will work. My demo of >>> a full scrolling football pitch used this system, which I believe you >>> saw many years a go. >>> >>> Dave >>> >>> ----- Original Message ----- >>> From: "Andrew Collier" <[EMAIL PROTECTED]> >>> To: <[email protected]> >>> Sent: Tuesday, May 20, 2008 9:50 PM >>> Subject: Re: Short, short questions >>> >>> >>>> Hi, >>>> >>>> I'm sceptical about this claim. I've never heard anybody say that the >>>> vector formed is big-endian - it's just you don't know the byte offset >>>> from which the interrupt vector will be fetched. (As Edwin says, it is >>>> usually 255 - which is odd so your 1-aligned table will usually work - >>>> but I don't know that Sam's hardware guarantees this). >>>> >>>> So the high byte comes from I, the low byte from the data bus; this >>>> forms a 16 bit address which will be incremented once (which is why >>>> the table needs 257 bytes, not 256). You could, at least in theory, >>>> read the vector address from even or odd overlapping entries, which is >>>> why the usual strategy is to pick a vector address whose low and high >>>> bytes are the same. >>>> >>>> The last IM2 interrupt routine I wrote looked something like this: >>>> >>>> ds ALIGN 256 >>>> IM2TABLE: equ $ >>>> IM2BYTE: equ im2table/256 >>>> >>>> IM2TARGETBYTE: equ IM2BYTE+1 >>>> for 257, DB IM2TARGETBYTE >>>> >>>> IM2TARGET: equ 257*IM2TARGETBYTE >>>> ds IM2TARGET-$ >>>> >>>> EX AF,AF' >>>> ... >>>> >>>> Andrew >>>> >>>> >>>> On 20 May 2008, at 21:16, David Brant wrote: >>>> >>>>> Mode 2 uses a table with 128 word address but as byte high,byte low >>>>> not the normal low, high bytes >>>>> >>>>> So if you set your org/dump address to &??FF (i.e. &??00-1) >>>>> >>>>> and then do >>>>> >>>>> DEFW mode2.i,mode2.i >>>>> >>>>> so you have 129 words. >>>>> >>>>> mode2.i: >>>>> di >>>>> push af >>>>> in a,(status.int) >>>>> ..... >>>>> ..... >>>>> ei >>>>> ret >>>>> >>>>> >>>>> >>>>> ----- Original Message ----- From: "Andrew Collier" >>>>> <[EMAIL PROTECTED] >>>>> > >>>>> To: <[email protected]> >>>>> Sent: Tuesday, May 20, 2008 3:22 PM >>>>> Subject: Re: Short, short questions >>>>> >>>>> >>>>> >>>>> >>>>>> The usual strategies are to use mode 1, or to use mode 2 with a 257- >>>>>> byte table all >>>>>> containing the same byte. >>>>>> >>>>> >>>> >>>> -- >>>> --- Andrew Collier ---- >>>> ---- http://www.intensity.org.uk/ --- >>>> -- >>>> >>>> >>> >> > APB Computer Services Ltd. 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