451061@UOTTAWA.BITNET (Valentin Pepelea) (01/28/89)
In <1989Jan26.210550.10129@gpu.utcs.toronto.edu> Bard Fowles (anakin@gpu.utcs. .toronto.edu) dares to write: > Oops! I'm afraid I don't pull *BERR if the Coprocessor ain't there. >Does anyone else. Boy ya learn something new every day. I must admit that >this makes perfect sense, Dale. Atleast his machine would GURU instead of >going off to la-la land. I humbly appologise. > > Brad > >BTW Valentin, does the board work now with the 881 installed? Like a charm! Even at 20Mhz with an Insider board under it. Due to the Insider's clock, the Lucas board gets to ride very high, so I can't put the RF shield back properly, but then who cares about the neighbor's TV reception? You know, I lost a month of my life on the missing 68881 problem. I still can't believe I did not realize what was going on when I noticed that *SENSE was unconnected. For people who can't afford to buy a 68881, I think that straightening out horizontally pin 18 on PAL U4 (*CPCS) and wire wrapping the socket's pin to Vcc through an unused SIP resistor should do the trick. Thus *CPCS will never get asserted, and the CPU space address will be handled by the rest of the Amiga. If the address is way off, a *BERR signal will be asserted. Otherwise some erroneous data will be fed to the CPU. If this trick does not work, then I could post a Kickstart patch to take away the problematic 68881 instructions. Patching Kickstart without the hardware hack would work too, but the Amiga would then hang whenever the CPU encounters an F-line instruction. Another solution is for you to redesign the Lucas board and use the *SELECT pin provided on the 68881. :-) That would also give you the opportunity to fix the U9 problem and maybe add a 68851 socket. (Oh please, oh please) Now a small question about the Lucas design. Could you not have connected the DSACK0/DSACK1 pins of the 68881 directly to the 68020 like I see it done on all Motorola manuals I have, instead of ORing them through your PALs? These two pins are automatically put into high impedance mode by the 68881 when they are not used by it. Valentin _________________________________________________________________________ "An operating system without Name: Valentin Pepelea virtual memory is an operating Phone: (613) 233-1821 system without virtue." Bitnet: 451061@uottawa Usenet: Look at the header - Ancient Inca Proverb Planet: Earth