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30 lines
2.0 KiB
30 lines
2.0 KiB
To: ZDE 1.6 Users
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From: Carson Wilson
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Date: 12 Nov 90
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About: Fix for control character display problems.
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Lee Rimar noticed that ZDE version 1.6 would not display control characters
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correctly on his equipment. Embedded control codes in his files such as
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control-S or control-Y were highlighted, but the characters didn't always
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correspond to those in his files.
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When Lee's friend Roger Bond discovered that the bug did not appear under
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ZSDOS, I was able to track down and eliminate the problem. As Roger Bond
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suspected, the bug is due to the differences between ZSDOS and standard
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CP/M. Apparently his "vanilla" CP/M software was using the AF' register.
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There is a long-standing controversy on this issue, but the ZSDOS team
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elected to play it safe and leave the "alternate registers" intact. In
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upgrading ZDE, I made the (mistaken) assumption that the AF' register would
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reliably store the value to be output in alternate video, and since many
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machines DO preserve AF', the mistake didn't show up on them.
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The next version of ZDE will fix the problem, but if you find that control
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characters are not displaying correctly on your computer you can also make
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the following changes to ZDE (version 1.6 ONLY) with DDT.COM or a patcher
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like Steve Cohen's ZPATCH:
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Address (100h offset) Old Value (opcode) New Value (opcode)
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--------------------- ------------------ ------------------
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389C hex 08 hex (ex af,af') F5 hex (push af)
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38A0 hex 08 hex (ex af,af') F1 hex (pop af)
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