I have to admit I was wondering the same. IM2 was necessary on the speccy because 0x38 was in ROM and couldn't be paged out but I see no reason not to use IM1 on the Sam. I'm quite happy to be told otherwise, of course :)
Geoff On Wed, 21 May 2008 13:50:14 +0100, "Adrian Brown" <[EMAIL PROTECTED]> wrote: > 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: sam-users@nvg.ntnu.no > 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: <sam-users@nvg.ntnu.no> > 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: <sam-users@nvg.ntnu.no> >> 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: <sam-users@nvg.ntnu.no> >>> 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: <sam-users@nvg.ntnu.no> >>>> 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: <sam-users@nvg.ntnu.no> >>>>>> 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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