To:       ZDE 1.6 Users
From:     Carson Wilson
Date:     12 Nov 90
About:    Fix for control character display problems.

Lee Rimar noticed that ZDE version 1.6 would not display control characters 
correctly on his equipment.  Embedded control codes in his files such as 
control-S or control-Y were highlighted, but the characters didn't always 
correspond to those in his files.

When Lee's friend Roger Bond discovered that the bug did not appear under 
ZSDOS, I was able to track down and eliminate the problem.  As Roger Bond 
suspected, the bug is due to the differences between ZSDOS and standard 
CP/M.  Apparently his "vanilla" CP/M software was using the AF' register.  
There is a long-standing controversy on this issue, but the ZSDOS team 
elected to play it safe and leave the "alternate registers" intact.  In 
upgrading ZDE, I made the (mistaken) assumption that the AF' register would 
reliably store the value to be output in alternate video, and since many 
machines DO preserve AF', the mistake didn't show up on them.

The next version of ZDE will fix the problem, but if you find that control 
characters are not displaying correctly on your computer you can also make 
the following changes to ZDE (version 1.6 ONLY) with DDT.COM or a patcher 
like Steve Cohen's ZPATCH:

    Address (100h offset)   Old Value (opcode)      New Value (opcode)
    ---------------------   ------------------      ------------------
    389C hex                08 hex  (ex af,af')     F5 hex  (push af)
    38A0 hex                08 hex  (ex af,af')     F1 hex  (pop af)