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The I/O port vector or the I/O port usage range start address of the EW904B is 390 Hex. Usage is from 390 Hex to 397 Hex. This didn't appear to be a handy place after I obtained a Sound-blaster Pro sound card (in the early nineties). The programmer didn't work anymore..... After I created a simple I/O address usage show utility (in Quick-Basic ! My PortDump program), it appeared that there was an overlap in I/O address usage due to a dummy addressing mechanism in the SB card. They didn't use all the needed lower address bits to point exactly (and only) at the midi channel near I/O 388-389. No, they killed all the possible use between 380 to 39F, 32 I/O addresses were made unusable. It was too complicated to solder on the (at that time: brand-new) soundcard, so I patched my EPROM programmer and the EPROM4 software. After some playing around with one's and zero's I found out that only ONE inverter in addressbit A8 would change the I/O vector from 390H to 290H: an ideal location. Making that modification was no problem at all for me, but how would the software be aware that something has changed?? After disassembling the software, which gave so much (listing) information, that there was hard to cope with. There was NO direct I/O port addressing, they used indirect pointers to a flag. That made it easy/ flexible for the programmers to change at a last moment. So I tried another approach. I looked with the Norton utils for a "90 03", the computer notation for the Hex 390 vector. I found only ONE location somewhere at 781AH and 781BH that looked hopeful and patched it to "90 02". After program start: I looked for the I/O address reply: 290Hex, bingo!!!! Software problem solved (no internal CRC check!), now soldering... I soldered a 74LS04 on top of U3, connecting only power pins 7 and 14. Cutting off all the other pins, only leaving a small piece to solder on. I only used pins 1 and 2, leave the rest floating. I also placed a jumper to choose between 290H and 390H. A photographic view is available of the change. Also see my schematic diagrams for more info how to do it. After changing both software and hardware: a testrun. OK, all worked well. Epilogue: With a few simple changes in both hardware and software it is possible to use the EW904B on the new address 290H. And make it easy switchable between 390H and 290H. No problem what so ever. Patched software for (only!) 290H probably available on this location. I also removed a typo error in one of the on screen menus. (Devive ---> Device). The patched software I used - only one vector byte change 03 ==> 02 and a typo removed, is over here. Walter Geeraert Vlissingen The Netherlands walterg@cumail.nl |
Copyright© 1990 - 2020 Walter Geeraert - All Rights Reserved
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