wilko@idca.tds.PHILIPS.nl (W.C. Bulte) (03/20/91)
I am experiencing some problems in upgrading a Mega 1 to a Mega 2.5. I did replace bank 1 consisting of 4 x 414256 (256Kx4 chips) by 16 x 411000 (1Mx1). The missing A9 line (not used on the 414256) is connected to the 411000 via a series R of 33 ohm. Result of all this: the ST recognizes the new bank 1 as a 128k bank, giving me a total of 640 kbytes. In addition a very interesting moving pattern of vertical bars appears on the screen. The bars are approximately 8 pixels wide. I get the impression that this screen pattern is due to non-refreshed dram locations. Apparantly the ST thinks (?) that 64 k drams are used for bank 1, resulting in a refresh cycle on 8 address lines (256 address refresh cycle) instead of the 9 address and 512 refresh cycle a 1Mbit memory cell requires. My question: does Atari use a different MMU chip in the Mega 1 with 414256 chips which cannot handle the 1Mbit cells? This would mean I am stuck with 1Mbyte. I'd love to see Spectre running with some more memory and Multifinder. Any help appreciated _ ______________________________________________________________________ | / o / / _ Wilko Bulte Domain: wilko@idca.tds.philips.nl |/|/ / / /( (_) uucp : [mcsun,hp4nl]!philapd!wilko * Philips Information Systems Nederland phone: 055-432372 fax: 055-432103 ____________________________________________________________________________