Conference hydra::amiga_v1

4162.0. "Fatter Agnus Blue(s)" by DECWET::DAVIS (You always get what you deserve) Fri Sep 28 1990 23:49

The scene:

	Amiga500 with Supra500XP scsi host controller(2Mb internal RAM),
	CSA Midget Racer(25Mhz 68882).  A500 has rev 5 motherboard.

The Plot:
	I recently aquired a Fatter Agnus with the intent of enabling
	and using 1Mb chip ram.  After installing the 8372A chip,
	enabling address line 19, and removing pin 32(_EXRAM) from the GARY
	chip socket, I powered on the 500 and lo a behold I see a "rolling" 
	blue screen with random noise emitting from my 1084s speakers.  
	After making sure my etch cut and other ministrations were correctly
	applied I removed my Supra500XP scsi controller and reapplied
	power.  Ho, I could now access 1Meg chip ram.  Hmmmm...I reinstalled
	the scsi controller with its internal expansion ram disabled and
	1meg chip ram was still present.  I re-enabled the 500xp internal
	memory and still got a rolling blue screen.  I replaced the Midget
	racer with the 68000, enabled the 500xp's RAM, powered up and
	found 1Meg chip ram and 2Meg expansion ram.  Replace the Midget,
	voila, blue rolling blue screen.

	Calling Supra was a complete waste, as I should have known it
	would be.(i will not bash supra, i will not bash supra...)  CSA 
	said that they would query their engineers and call me back.  In
	the mean time I trying to get the Amiga Hardware docs so I can figure 
	what _EXRAM does and how it relates to the CPU and the expansion bus 
	in general.  I am writing this on my A500 with the 8372A installed but 
	configured as a "normal" fat Agnus.  Works fine this way. :^{



Query:	Can someone give me a general description of "_EXRAM"?


    mark

    You might want to post the question on comp.sys.amiga.hardware - Dave
    Haynie has been very responsive to questions such as this. 
    
    John

    Sorry, but the addition of the 1MB CHIP RAM to an A500 is NOT SUPPORTED
    according to CMB.  There are timing problems and the installation
    of the chip invalidates the warranty.
    
    Nasty, huh!
    
    TOPGUN