rminnich@udel.EDU (Ron Minnich) (02/05/88)
I am trying to add some memory to an A1000. For several reasons the hardware is not asserting DTACK. This brings up a question: something else is! Is there a watchdog timer in the custom chips that automatically asserts DTACK after x cycles? I guess there would have to be, else if you addressed non-existent memory the thing would hang. Can anyone fill me in? The hardware manual is not helpful in this case. I am hoping to hear that DTACK is not just asserted always by the hardware as this memory cycles in 675 ns (i.e. slowly) so i really need DTACK to work right. -- ron (rminnich@udel.edu)
ebr@io.UUCP (Evan B. Ross) (02/05/88)
The hardware manual states that the amiga always asserts dtack/
by itself unless you assert the xrdy line. (I think it's called
xrdy, it might be 'hold'. My manual isn't handy.)
--
There's sparks a comin' outa' my head!!!
...!harvard!umb!ileaf!ebr Evan B. Ross, Interleaf, Cambridge, Ma
...!sun!sunne!ileaf!ebr (617)577-9813 x5570phils@tekigm2.TEK.COM (Philip E Staub) (02/06/88)
In article <1107@louie.udel.EDU> rminnich@udel.EDU (Ron Minnich) writes: >I am trying to add some memory to an A1000. For several reasons >the hardware is not asserting DTACK. This brings up a question: >something else is! Is there a watchdog timer in the custom chips that >automatically asserts DTACK after x cycles? I guess there would have to >be, else if you addressed non-existent memory the thing would hang. >Can anyone fill me in? The hardware manual is not helpful in this case. >I am hoping to hear that DTACK is not just asserted always by the hardware >as this memory cycles in 675 ns (i.e. slowly) so i really need DTACK >to work right. > >-- >ron (rminnich@udel.edu) Ah, but the hardware manual *is* helpful. You just have to know what to look for. I don't know the exact page, but what happens is that that Amiga is *not* expecting to have DTACK asserted by any expansion device. DTACK is generated internally, unless you sit on a busy line (I think it's XBUSY, or something like that, no manual handy) to say you want to stretch the bus cycle. There is also a spec as to how soon after the bus cycle begins that you have to assert the busy line. This looks (at least to me) like shades of Intel processors(!), which assume that bus cycles have completed successfully unless your hardware sits on a bus error or wait line to say that it failed or needs to be stretched. Hope this helps. Phil -- ------------------------------------------------------------------------------ Phil Staub "I do NOT approve. I merely said I UNDERSTAND." tektronix!tekigm2!phils - Spock phils@tekigm2.TEK.COM
hah@mipon3.intel.com (Hans Hansen) (02/06/88)
In article <1107@louie.udel.EDU> rminnich@udel.EDU (Ron Minnich) writes:
$I am trying to add some memory to an A1000. For several reasons
$the hardware is not asserting DTACK. This brings up a question:
$something else is! Is there a watchdog timer in the custom chips that
$automatically asserts DTACK after x cycles? I guess there would have to
$be, else if you addressed non-existent memory the thing would hang.
$Can anyone fill me in? The hardware manual is not helpful in this case.
$I am hoping to hear that DTACK is not just asserted always by the hardware
$as this memory cycles in 675 ns (i.e. slowly) so i really need DTACK
$to work right.
DTACK in the Amiga is controlled by the PALs in the A1000 and by the gate
array in the A500 and A/B2000. All interfacing must live within the alotted
time. The reason for this is to allow the copper (Agnus) to run at twice
the bus bandwidth of the 68000.
$--
$ron (rminnich@udel.edu)
Hans hah@inteloa -or- hah@inteloa.intel.comrminnich@udel.EDU (Ron Minnich) (02/09/88)
In article <2487@tekigm2.TEK.COM> phils@tekigm2.UUCP (Philip E Staub) writes: >Ah, but the hardware manual *is* helpful. You just have to know what to look well you are right. I missed the proper page. The signal is XRDY. You pull it low withn 60ns of AS/ and hold it low till you are ready for DTACK/ to do its thing. Sorry. I looked in my Hardware manual instead of my Schematics and Expansion spec. manual ron -- ron (rminnich@udel.edu)
daveh@cbmvax.UUCP (Dave Haynie) (02/10/88)
in article <1107@louie.udel.EDU>, rminnich@udel.EDU (Ron Minnich) says: > > I am trying to add some memory to an A1000. For several reasons > the hardware is not asserting DTACK. This brings up a question: > something else is! Is there a watchdog timer in the custom chips that > automatically asserts DTACK after x cycles? I guess there would have to > be, else if you addressed non-existent memory the thing would hang. > Can anyone fill me in? The hardware manual is not helpful in this case. > I am hoping to hear that DTACK is not just asserted always by the hardware > as this memory cycles in 675 ns (i.e. slowly) so i really need DTACK > to work right. > ron (rminnich@udel.edu) This may have been answered already (though GRR's been as busy as I have), but ordinarily, /DTACK is driven by the system. An expansion board has three options concerning /DTACK. The simplest is just to obey the /DTACK the system gives you, but that's not always possible. The second option is to delay the system generated /DTACK by asserting XRDY when your board is selected. This will hold off /DTACK, but it must be issued very quickly, like 50ns-60ns into the cycle. Your third option is to assert /OVR when your board is selected. This will cause the Amiga (any variety) to tri-state /DTACK so you can drive it yourself. BTW, the hardware manual isn't helpful on any expansion issues. There are two books published by Commodore-Amiga (available only from CATS) that detail hardware design. The first is "Schematics and Expansion Specifications", which covers the basic expansion design, A1000 schematics, casework, etc. This is about $20.00. The second is "A500/A2000 Technical Reference Manual", which contains everything in the A1000 book except A1000 specific stuff, plus notes specific to A500 and A2000 machines (mechanicals, schematics, design guidelines). This one is around $40.00. -- Dave Haynie "The B2000 Guy" Commodore-Amiga "The Crew That Never Rests" {ihnp4|uunet|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy "I can't relax, 'cause I'm a Boinger!"