wfs@sauron.Columbia.NCR.COM (wfs) (04/22/88)
I recently borrowed a 68020 to 68000 adapter to try out in my 2000 but failed
to get it to work. The 2000 began its powerup sequence (3 flashing screens)
but failed to proceed any further than that.
The board is made by TORCH computers for CSA and plugs directly into the
68000 slot. On board are 68020 and 68881 sockets, 2 pals and 3 other chips
( 1 piggyback ). The clock speed remains at the system speed of 7.14 MHz.
I was wondering if anybody has had experience with this board or similar
boards and what a person must do (i.e. system eprom modification???) to get
a 68020 adapter like this to work.
My thoughts of the problems offhand are that a system instruction for the
68000 is being executed and interpreted by the 68020 as garbage. This, to
me, would be a relatively simple fix. My other thought is that after the
three screens flash during startup, the DMA controllers begin to kick in and
are interfering with the 68020's instruction stream.
Any thoughts on this subject would be much appreciated.
BTW, I do have tools such as 68020 logic analyzer, scope, and NCR Towers at
my disposal and am willing to get my hands dirty ( so to speak ).
Bill Stonecypher
NCR Corporation
wfs@ncrcae.Columbia.NCR.COMdaveh@cbmvax.UUCP (Dave Haynie) (04/29/88)
in article <1060@sauron.Columbia.NCR.COM>, wfs@sauron.Columbia.NCR.COM (wfs) says: > My thoughts of the problems offhand are that a system instruction for the > 68000 is being executed and interpreted by the 68020 as garbage. This, to > me, would be a relatively simple fix. My other thought is that after the > three screens flash during startup, the DMA controllers begin to kick in and > are interfering with the 68020's instruction stream. It's certainly a hardware problem, the software doesn't have any trouble with a 68020 running at any speed. Even at the same clock speed, some of the 68000 features have to be emulated pretty closely by the interface logic, or you'll get in trouble. If I had to venture a blind guess, I would guess the problem is in the 68000 DTACK to 68020 DSACK translation. Specifically, the 68000 samples DTACK on the falling edge of S4, while the 68020 samples the DSACK lines on the falling edge of S2. If DTACK comes along before S4, which is perfectly legal in an Amiga system, the 68020 could get a DTACK too early and try to terminate the memory cycle before the proper time. Other places to look would be in the AS or E/VPA/VMA logic on the interface board. The 68020 asserts AS during S1, while the 68000 asserts AS during S2. The difference may confuse the Amiga system, so AS should really be held off until S2. The 68020 also doesn't have the E clock logic that's on the 68000, so this had better be emulated by the tower. Aside from that, running the 68020 at the same speed as the 68000 should remove most of the other problems that show up when the 68020 is going faster than the 68000. Hope this can be of some help. > Bill Stonecypher > NCR Corporation > > wfs@ncrcae.Columbia.NCR.COM -- 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!"