CompuServe Messages

BM <<have the A501 in one of my 500s, and an equivilant in the other. I have no intention of removing them, so converting them to address the one meg of chip RAM would be no problem.>> Good! You have most of the work already done — the getting of an 8372A and an A501 expansion. However, I would use the real A501, since many of the 3rd party A501-clones lacked the option to be used as CHIP RAM. The first thing to do is toggle the Agnus into 1-meg mode. Look to the right of the 68000 CPU and just above the KickStart chip. You should see three small, silver, square, solder pads. This is the JP-2 jumper. The middle pad will have a thin solder trace connecting it to the bottom pad, this is the 512K mode. Cut the trace between the middle & bottom pads, and use a bit of solder to create a trace between the top & middle pads. This flips the Agnus to 1024K mode. Now you must re-configure the A501. This is the hardest part, since the rev.5 A500 didn't have the JP-7 jumper used for re-configuring the A501. You will have to find the trace that connects the EXRAM signal of the A501 to the GARY chip. When connected, the A501 is FAST RAM, when it is cut the A501 is configured as CHIP RAM. I believe the trace to cut runs from pin #32 of the 56-pin A501 slot to pin #32 of the GARY chip. It is best to cut the trace at the spot just *ABOVE* a pad (small silver disk) by the 56-pin connector. On the rev.5 motherboard this pad is located by counting 8 positions down from the top of the connector (or 3/4th inch). The pad will be the first of several dierctly the the left with a trace going toward the Gary chip. — BM <<What is the difference between the OCS, ECS and AGA chip sets? I know the AGA has greater graphics capability, but I'm fuzzy on the OCS-ECS differences (I take it from your message, that one difference is the 8370 vs 8372A).>> The original Agnus was the #8361, a thin DIP chip that looked just like the Denise & Paula. This was the version used in the A1000. The A500 & A2000 used a new 'FAT' chip design for the Agnus. This new square chip internalized several support chips (like the genlock support), but added no new features. There were two versions, the NTSC (#8370), and the PAL (#8371) used in Europe. This two versions are part of the Original Chip Set (OCS). Commodore then developped the Enhanced Chip Set (ECS). This was a new FAT Agnus & Denise. They could be dropped into most existing A500s & A2000s adding several immediate enhancements, with added abilities with re-configuring of the hardware. This ECS Agnus (#8372a) combined with the ECS Denise (#8373) added: – new memory limits (1024K for A500/2000, 2048K for A3000) – new Blitter Range (32K by 32K pixels in size) – new mode resolutions (Superhires, 1280 pixels horizonal pixels per scanline on standard NTSC & PAL displays) – new monitor scanrates (640×480 non-interlaced screens (VGA)) – new Genlock capabilities – Chromakey (allows any color reg to control video overlay) – BitPlaneKey (allows any bitplane to enable the video overlay) – BorderBlank (creates a transparent "frame" surrounding the active area.) – BorderNotTransparent (makes an opaque "frame" surrounding the active area.) The #8372b ECS Agnus was the version for the A3000. This version removed the genlock to external chips to make room for supporting more CHIP RAM. Using this version in an A500/2000 requires a extra curcuit board for adding the missing genlock and connecting the extra CHIP RAM. The #8375 ECS Agnus was a version of the #8372b, with the pins re-arranged for a cleaner motherboard design. It was used in the A500-PLUS, and some versions of the DKB MegAchip expander for the A500/2000. — BM <<Any idea what the B-52s and their Rock Lobster song have to do with Amiga? I guess they could have been listening to the song when they were designing the thing, but it seems like a strange thing to do.>> The designers were fans of the B-52s, and did alot of strange things with the Amiga designs. Hidden messages in the Workbenches, hidden icon showing signatures of the designers, the signatures of the designers in the A1000 case (including a dog's paw). Ron.