aptr@ur-tut (The Wumpus) (07/19/88)
I tried mailing this reply directly, but there seems to be a problem with our path list, and I can not get this letter through. It also may be of some interest to others with 6300s. >From: sunybcs!ur-tut!aptr@rutgers (The Wumpus) >To: philabs!ttidcb!billh >Subject: RE: EGA Cards in 6300s (and why the problems, long) In article <2284@ur-tut.UUCP> you write: >I also beleive they solved the hardware problem that caused >difficulty in running EGAs on the old 6300's. I am interested in anything you might know about this. I have "an old 6300" and I am looking into cheap ways to get PCpaint, Lotus, games, etc. to use the higher resolution display mode. Any feedback would be appreciated. I don't have a copy of the article you are quoting, and I have written several things on EGA cards recently, so if I repeat something, please don't be offended. If you have a "classic" 6300 you have several choices in adding an a higher resolution graphics card to the machine. All of these involve the disabling of the indigenous display card. If you have a lot of money to play with, you can go out and buy a VGA card and a new monitor. You can also go out and buy a generic EGA card and a new monitor. Both of these will cause you to loose the AT&T specific modes (640x400, Tiny Text). There are currently two products that I know of that allow the use of the "classic" AT&T color monitor (318). One of the boards is made by TBS. This will give EGA, but will not keep the AT&T modes. The other solution is the AT&T VDC 750. This graphics card gives EGA and AT&T modes plus a 640x400 16 color mode. This latter mode is NOT DEB. I am currently using the VDC750 and I have found it to work very well with the old monitor. The only draw back with keeping the old 318 monitor is that it only supports 16 colors, not the 16 out of 64. This has to do with the electronics of the monitor itself. Any EGA card may have problems resulting fromwo things. The first is the way that the AT&T 6300's Bus Convert card works. This is the card that is responsible for controlling how both the 16 bit and 8bit busses of the computer can be used. The card is actually what you plug extra cards into (ie. The board with the slot connectors.) When Olivetti designed the controller, they were presented with a problem: How do you handle 16 bit read/writes to an 8 bit board. Their solution was simple. You first send the low order 8 bits out on the 8bit bus, and then you send the high order bits. (I may have the order reversed here.) When IBM later faced the same problem, they opted to send the bytes in the reverse order. This alone should not effect any 8 bit card because why would you want to send 16 bits of data to an 8 bit card. Well, some programmers (namel hackers) thought that they could use the order to their advantage. Some programms only used 16 bit bus access because the programmers knew how IBM designed the bus and depended on the byte order. One method was to move the information that was to be transfered to the high order byte of the AX register (AH) and then do a 16 bit write. Since the high order byte was sent first on a true IBM, the other byte (AL) did not matter to an 8 bit board. In the AT&T 6300, the low order byte goes first and the board recieves garbage. Some boards, mostly EGAs, need two bytes sent for commands. The first byte is typically a command and the second byte is an argument. Some programmers used 16 bit writes to send commands to EGA cards. Since the bytes get reversed in the 6300, the EGAs get garbage. In both of these cases, the problems could have been avoided if 8 bit I/O to the bus was done. It should be noted that the problem is not limited to the Olivettis (AT&T 6300, Xerox 6064, etc.). A similar problem exists in the early IBM PC that only had 64k on the motherboard (I don't know the specifics of their problems). In the later 63xxs (6310, 6386 WGS, 6300 WGS), the bus controller was changed to allow the computers to be more compatible. This changed envolved a complete revamping of the controller boards on the machines. I do not currently know if the controller in the 6300 WGS will work in a 6300. It is one of the solutions to the problems I am looking into, but even if it doesn't, don't loose all hope yet. Only a few programs are affected by the bus incompatibility. Most of these programs also can use the AT&T 640x400 mono mode, so if you are running a VDC750, you can still use the program. I am also working on a possible fix to the bus problem. It envolves the changing of the PROM that controls data movement in the bus controller. If I am right, by making a few small changes to the code in the PROM, I can reverse the order of 16 bit read/writes to the 8 bit bus and make it IBM compatible. I hope to be trying out the fix in the next week or so, depending on how soon I can get a new PROM burned and tested. If you are interested in the fix, I can let you know how it works out. Now, I had better summarize to make sure I said everything I wanted to. There are several EGA solutions. All of them require disabling the display card i nthe 6300. Some of them allow you to keep the old monitor (TBS EGA, VDC750), and the VDC750 is the only one supporting all of the old AT&T modes. The problems with EGA cards in the 6300 stem from the way 16 bit I/O to 8 bit boards is done and how dependent software programs are to the "IBM order". The problem has been solved in later machines by the redesigning of the bus controller card. I think I have come up with a solution for older machines, buy it has not been tested and requires the replacement of one PROM on the bus controller. There are also software methods to solving these problems, but they require the patching of offending programs. If you are interested, I can send you some information on what to look for and what to try and change. If you have any more questions, please feel free to contact me. John Werner aka The Wumpus UUCP: {cmcl2!decvax}!rochester!ur-tut!aptr BITNET: aptrccss@uorvm Internet: aptr@tut.cc.rochester.edu Disclaimer: "Who? When? Me? It was the Booze!" - M. Binkley ~p -- The Wumpus UUCP: {cmcl2!decvax}!rochester!ur-tut!aptr BITNET: aptrccss@uorvm Internet: aptr@tut.cc.rochester.edu Disclaimer: "Who? When? Me? It was the Booze!" - M. Binkley