ZRLE Documentation
                                       by
                                  Norm Lehfeldt


     What is an RLE Graphic?

     An RLE Graphic is an image stored in a form that is compatible with any
     computer display that is dot-addressable and offers resolution of at
     least 256X192 pixels. There is no gray-scale -- pixels are either on or
     off. The storage format uses only ASCII characters with codes from
     32 (space) to 127 (del). This range of codes insures that no control
     codes are part of the file and so the file can be transferred from
     computer to computer with no unexpected results.

     RLE encoding programs have been written for many popular computers, but
     until there is a drawing program for the Z88 -- a highly unlikely
     development -- an encoding program for it seems unnecessary.

     ZRLE, though, is a servicable program for decoding, displaying and
     printing RLE graphics which have been created on other computers. BBS's
     and some commercial data bases can be sources of such images.

     How do I use ZRLE?

     Before you can use ZRLE, you must have PAT2PCW, a BASIC patch that
     implements graphic displays and screen dumps on the Z88. PAT2PCW can be
     downloaded (as can many other valuable files and programs) from Phil
     Wheeler's Z88 BBS in Torrance, CA -- (213) 370 2754.

     Install the graphic facilities with the statement, CHAIN"PAT2PCW.BAS".
     (Throughout this discussion I will omit the RAM specification from LOAD
     and CHAIN statements. Such specification must be included if the file
     or program is not in the default RAM or EPROM).


     Once PAT2PCW is installed, invoke ZRLE with the statement, CHAIN
     "ZRLE.BAS". The rest is easy -- simply follow the prompts.

     You must, of course, have an RLE file or two in the Z88's memory
     before you can see a picture.

     Things to keep in mind while using ZRLE.

     Since the Z88 graphic display is only 64 pixels high, the image is
     displayed in three sequential sections. Print them out and paste them
     together to see the whole image.

     When asked for a file name to decode, you must include a RAM or EPROM
     specification if the named file is not on the default device.

     The program makes no validity check on the files to insure that they
     are in fact RLE graphic files. If you enter the name of another type of
     file, the results are unpredictable -- except that the program will
     ultimately crash!

     A file name that does not match anything in memory will crash the
     program. Restart with "RUN."

     If you do not have an Epson-compatible printer connected, avoid
     pressing "P" at the prompt.

     How can this program be improved?

     If you are smarter than I you can convert the main processing loop,
     lines 50 to 180, to machine language. We would all appreciate the
     speedup.

     The printer driver in PAT2PCW issues spurious line feeds which require
     cutting and pasting the printouts. This needs to be fixed.

     The printer driver also produces vertically elongated images on 24-pin
     printers. I would like it if someone could fix this, too!

     If you have questions or comments on this program, I will try to answer
     them. Leave me a message on the Z88 BBS or on CompuServe.

     Enjoy the program.

     Norm Lehfeldt, CompuServe ID# 72466,3273
     San Francisco, CA
     3/16/90