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ZPLOT Version 1.0 DOCUMENTATION ZPLOT USER'S GUIDE General Information Running ZPLOT Application Programming ZPLOT Commands Pitfalls and Limitations Error Messages INSTALLATION INSTRUCTIONS Sizing the Memory Map Printer Settings GENERAL INFORMATION ZPLOT is a program that can produce high resolution graphics on dot matrix printers. It reads a disk file created by the application program which is used to describe the pictures to be printed, and prints them on an Epson- compatible dot-matrix printer. The application program "plots" by writing simple plot commands to a disk file, which is later read and printed by ZPLOT level driver. This file is the key to the whole system, because it makes the application program independent of the plotting device and vice versa. It also makes it possible to plot pictures that were created on different computers or to plot the same picture on different types of hardware, such as CRT's and printers. ZPLOT will work with any printer supporting Epson bit-mapped graphics which includes most of the dot-matrix printers on the market today. ZPLOT lets you treat your printer as if it were a plotter capable of true vector graphics. All future versions of ZPLOT will support the same basic file format and will be compatible with each other. ZPLOT was derived from PLOT33 by Tom Speer and uses an identical file format. This documentation describes how to get ZPLOT installed, specifies the format for the disk file of plotting vectors (".VEC" files), and gives an overview of the user program interface. You will probably want to briefly skim over the descriptions below and go right to the Installation section. Capabilities ZPLOT's command set includes instructions for device independent graphics and commands that provide access to the unique capabilities of specific devices. The device independent commands are patterned after a pen plotter's characteristics, with a rudimentary capability for filling areas on raster scan devices. These device independent commands include the capability to move to a point without plotting, to plot points and straight line segments, to change the current color, and fill in a trapezoidal area. More complex areas can be decomposed into simpler regions for filling. The device dependent commands include the ability to plot/print a string using hardware character capabilities. The Upload command can be used to upload the red-green-blue values used for the color table on color graphics terminals (or stipple patterns to be used for "colors" on monochrome devices as in ZPLOT). The Erase command will clear the screen, establish the background color, or advance the page, as appropriate for the type of plotter or display. An Output command is used to produce hardcopy output or print the memory map. A general instruction that can be used to extend the command set for any other non- standard command required rounds out the device dependent commands. As mentioned above, all future updates to this version of ZPLOT will be compatible with the existing plot files and high level software. Future drivers are also planned for creating and interpreting the vector command file on mainframe computers using Calcomp or Tektronix plotters and terminals. As much as possible, the eXtend command should be used for adding neat new features for your printer or taking advantage of the capabilities of more advanced devices. This will make it possible to maintain the file format as a means of exchanging information without a fatal proliferation of exclusive versions. Acknowledgments ZPLOT is based on PLOT33, by Tom Speer, and is basically a Z80 version of that program, with rudimentary Z3 support (allowing .VEC files to be accessed from a different drive/user). The extreme compactness of Tom's .VEC file format was the primary attraction, especially if the format is to be used in real-time applications, such as driving a CRT display. RUNNING ZPLOT To use ZPLOT, first create a sequential disk file of plot commands. These are described fully in the next section. Then execute ZPLOT by typing: ZPLOT ifn [ofn] ifn is the input file name. A file type of .VEC is assumed if no file type is given. [ofn] is an optional output file name. If no output file is given, the output from ZPLOT will go directly to the printer (LST: device). If an output file is specified, all of the information normally sent to the printer will be stored in the disk file instead. In this case, no printed output will be produced. PRINT or some other utility may be used to print the picture. This option is useful for making multiple copies or for including graphics in the middle of text files. The default output file type is .PLT . Note: Output files are large- typically 40 to 60k. Be sure to leave enough space on the disk for the entire file. APPLICATION PROGRAMMING Application programs "plot" by writing the appropriate plot command to a disk file. This file later becomes ZPLOT's input file. The plotting area is a square, with the coordinates (0.0 , 0.0) located at the bottom left corner, and the coordinates (1.0 , 1.0) located at the upper right corner. These coordinate values are independent of the resolution or aspect ratio of the plotting device. ZPLOT converts these values to the actual number of rasters (dots) used by the printer to produce a square plot approximately eight inches on a side. All plot commands are written to disk one after the other, with no spaces or delimiting characters between them. Each command consists of an ASCII character followed by the binary data which it requires. Many languages, such as BASIC, insert extraneous characters, such as carriage returns or line feeds, at the end of each block written. Because of this, plotting commands should not be split between blocks, as these extra characters will be interpreted as data in a command. If the extraneous character occupies the position of a command character, however, it can be detected and ignored. The current application programs output plot commands in 128 byte blocks. If a command will not fit in a given block, the block is written to disk, and the next command written in a new block. This ensures that the extraneous characters will fall between commands where ZPLOT can deal with them. When using fixed length blocks or records, each can be padded with "N"'s to preserve its length before it is written. The recommended command sequence to produce a picture is: 1. Set the color to black or white (color values 127 or 0) for a background. Usually white is used. 2. Erase the picture to initialize the memory map area and establish the background. 3. Set the color value for plotting. Usually black (127) is used. 4. Establish a starting point by using the Move command, plotting a single point, or plotting a line segment using the Draw command. 5. Proceed to create the remainder of the plot. The Increment command is recommended when one line segment is connected to the previous one, as in a curve. 6. Be sure to include an Output command to print the final plot. 7. Use the Quit command to stop plotting. ZPLOT will terminate automatically at an end-of-file, but with an error message, and without printing the picture. ZPLOT COMMANDS Each command is of the form: Adata "A" represents the single ASCII character as explained below. "data" represents 0 to 86 bytes of data required for the particular command. Usually this consists of fixed point numbers giving the coordinates of points or ends of line segments. No spaces or delimitating characters are used between fields within a command or between commands. The individual commands are described in Table 1. The data values required for the plot commands are not ASCII character strings, but are binary byte values. The coordinate values are 16 bit fixed point binary fractions. This makes the format particularly easy to use in application programs written in assembler. Different word lengths, internal storage formats, and file structures have to be considered when constructing the command file on mainframes and microcomputers not based on the Z80 family. For instance on 68000-based machines the reversed byte order should be taken into account. The ability to structure a file as a byte stream is the basic requirement. The Dump utility can be used to ensure that the contents of the file are what you expected. The 16 bit data values are stored with the low order byte first (swapped format). This is the standard way of storing words for the Z80 processor. Note that because the data values are not ASCII strings, the TYPE command will not properly display the file at the console. TABLE 1 PLOT COMMANDS Command Length Name Character Data (bytes) Command Data Description ---------------------------------------------------------------------- Color C b 2 8 bit integer specifying one of a range of colors. 0 indicates white, 127 indicates black. Draw D X1,Y1, 9 Coordinate pairs for ends of line segments. X2,Y2 Erase E 1 Sets the entire ploting area to the currently selected Color value. Fill F X1,Y1, 11 Coordinate pairs for ends of line segment X2,Y2,Yf and horizontal level (Yf) defines area to be filled in with currently selected color. Incre- I X,Y 5 Coordinate pair for end of line segment. ment Starting coordinate is last point plotted. Move M X,Y 5 Coordinate pair for new "pen" position. No-op N 1 Ignored. Used as space filler in sequence of commands to exactly fill a disk record. Output O 1 Causes current picture to be printed. Point P X,Y 5 Coordinate pair for point to be plotted. Quit Q 1 Commands normal termination of program. String S X,Y, 6 Coordinate pair for start of character string to string to be printed. String 86 MUST end with a Carriage Return. Text T string 2+ String of arbitrary length. String MUST end with a <NULL> (00H) character. Upload U N, 3 N is a 16 bit unsigned integer giving the values to number of values to follow. Values N+3 specify basis for creating new "colors". eXtend X N, 3 N is a 16 bit unsigned integer giving the values to number of values to follow. Values are N N+3 bytes of whatever data is necessary. The following sections describe the way in which the commands have been implemented in ZPLOT Version 1.0. Other drivers may not implement them in exactly the same way, but the general sense should be preserved. Colors are simulated in ZPLOT by using stipple patterns. These patterns apply to all points, lines, and filled areas. These patterns are based on 8 dot by 8 dot cells that tile the entire picture area. Imagine cutting each figure out of a sheet entirely covered with the desired pattern and then pasting it on the plot in progress. This gives a general idea of the way in which the patterns work. Three different methods of generating the patterns are used. Each method trades off the memory required to store the basic patterns with the ability to specify exactly what the pattern will look like. When a Color command is given, all subsequent plotting will be done with that "color", or pattern, until it is changed with another Color command. The Color command simply acts as a selector to pick one of a number of colors or patterns that are currently available. A color code of 0 corresponds to white. Lines and filled areas plotted with this color will absolutely erase any dots that were previously plotted. Color codes from 1 through 48 will produce cross hatched patterns that generate checkered areas and other distictive patterns. Codes from 49 to 63 correspond to 15 special patterns that can be programmed to exactly match any desired pattern based on the 8 x 8 dot cells. Codes from 64 through 127 are generated using an ordered dither matrix, in which each succeeding code is the same as the previous one, except for one more dot per cell being plotted. These are currently set to generate a range of shades of gray. All of these patterns can be changed under the control of the application program by using the Upload command. Each dot is added to the memory map by OR'ing it with the dots previously plotted. Each subsequent figure does not totally obscure the existing picture. For example, suppose that a gray shade is being used that consists of every other dot being plotted. The dots that are not plotted will not cause the existing dots to be set to white if they were previously plotted. Negative color values (-1 to -127) will use the same pattern as their positive counterpart, but will be XOR'ed with the existing picture. This means that the figure will be plotted black on white or white on black, depending on what the existing background is. Plotting the same figure twice with a negative color value will have no net effect on the picture. Filling the whole picture with - 127 (negative black) will have an effect like making a photographic negative. The String command is used to mix printed characters and graphics. The characters are printed using the printers normal character set. No facility is provided in ZPLOT to send <ESC> codes or control characters to the printer to change character sizes or font styles. The string is printed starting near the coordinates given in the command. The exact position will vary, but the first character will cover the coordinate location. The ambiguity comes from the fact that most printers can only print characters at their normal location on the page, and can't use graphics commands to position the characters at any arbitrary place on the line. In addition, a printed character can't be part on one line of print and part on another. Therefore, ZPLOT computes the closest character location to the desired coordinates and begins the string there. The Text command will immediately send a text string to the printer when the command is encountered. This is quite different from the String command, because the text is not put in the memory map and is not part of the picture. This command is useful for positioning the plot on the page, for printing titles and headers, and for advancing to the next page after the plot is printed. Any ASCII characters may be included in the string, including control codes, escape sequences, carriage returns, and linefeeds. The only exception is the null character, 00H, which is used to signal the end of the string. The string may be of any length. This makes it a convenient way of imbedding a figure in the middle of a document, since all of the text above the figure can be included in one Text command, as can all of the text after the plot. Any text to be included in the plotting area itself must be entered one line at a time with the String command. Upload Command The Upload command deserves some special attention, because it is the least standard of all of the commands currently implemented. Most dot matrix printers can, of course, only print in black. To give these printers a "color" capability, different patterns have been programmed to produce shades of gray and distinctive cross hatched patterns. The cross hatched patterns are intended to be used for bar charts, dotted and dashed lines, etc. The shades are the closest that ZPLOT can come to true colors. The special patterns are very useful for matching patterns produced by other systems, and for anything that just can't be done with the other two methods. The Color command acts as a selector to choose between the pre-defined patterns. The Upload command is only needed if the default patterns are not capable of producing the desired effect. It will redefine the patterns from which the Color command can select. The cross hatched patterns are based on seven bytes that provide the basic patterns in both the vertical and horizontal directions for each cell. One byte from the seven is selected as the X pattern and one byte from the seven is selected as the Y pattern. The X pattern is extended vertically throughout the cell, and the Y pattern is extended horizontally throughout the cell. The two patterns are reversed (XOR'ed) where they cross. The effect is much like weaving a plaid material. The selection of the bytes for the X and Y patterns is made by the Color code. The lower three bytes of the Color value select the X byte and the next three bytes select the Y byte. The best way to determine the exact apperance of each pattern is to experiment by filling blocks with different patterns. If the existing patterns are not acceptable, new ones can be Uploaded. Set the number field, N, to 07H. The next seven bytes will be the bytes that form the basis for the patterns. Each bit corresponds to a dot in the pattern. A byte of 07H for the X pattern would produce the pattern .....*** . If an F0H is used for the Y pattern, the final cell will look like: *****... *****... *****... *****... .....*** .....*** .....*** .....*** The second type of pattern, used for the 15 special patterns, is specified by giving the 8 bytes that produce the pattern. Thus, the sequence 00H 00H 99H 00H 00H 99H 00H 00H will produce the pattern: ..*..*.. ........ ........ ..*..*.. ..*..*.. ........ ........ ..*..*.. These patterns are uploaded by specifying 120 for N followed by the 120 bytes that define all 15 of the special patterns. No facility is provided for just uploading one set of 8 bytes. The other method for producing patterns for "colors" is an eight by eight byte dither matrix. In this method, each byte in the matrix corresponds to one dot in the eight by eight dot cell. These cells tile the picture plane, as before. Color code values from 64 to 127 are used to select the 64 patterns created by the dither matrix. Each element of the matrix is assigned a value from 63 to 126. If the Color value is greater than the value in the matrix corresponding to a given dot, that dot is plotted. Thus, 127 is greater than all of the elements, and all dots in the matrix will be plotted, producing black. If each element of the matrix is assigned a different value, then a unique pattern will be associated with each Color value. For example, if the Color code is 64, only the element with a value of 63 will produce a dot. If the Color value is 65, those elements with 63 and 64 will produce dots. As the Color code is increased, and figures are plotted, another dot in the "tile" has the potential for being plotted. The existing arrangement of values in the dither matrix is designed to produce shades of gray with a minimum appearance of organized patterns. This matrix came from Foley and Van Dam's "Fundamentals of Interactive Computer Graphics". A common use of the Upload command is to change the matrix to provide diagonal patterns for shading areas. This would produce a pattern that looks like (for four cells): //// //// //// //// To design an Upload sequence for a given pattern, lay out a matrix representing a single cell. Start with 63 and place the numbers in the matrix in the pattern desired. For example, a cell from the diagonal pattern above could be created from the matrix: 63 111 85 103 75 115 93 95 112 64 104 86 116 76 96 94 79 105 65 117 87 97 77 121 106 80 118 66 98 88 122 78 71 119 81 99 67 123 89 107 120 72 100 82 124 68 108 90 91 101 73 125 83 109 69 113 102 92 126 74 110 84 114 70 To see the pattern, look at the matrix part way through its construction: 63 75 64 76 65 77 66 78 71 67 72 68 73 69 74 70 For this matrix, the Color code 79 will result in all of the above points being plotted in any filled in area, and the diagonal pattern will emerge. Once the matrix is constructed, the Upload command to load it is formed by an ASCII "U" followed by 40H, 00H to indicate 64 bytes to come, and finally 03H, 6FH, etc., the bytes of the matrix. The matrix is read in one row after another ( the [1,1] element followed by the [1,2] element, ..., to the [1,8] element, then the [2,1] element, ...). All of the matrix values are binary 8 bit values. To summarize the Upload command: The Color codes from 1 to 48 are produced by cross-hatched patterns based on eight pattern bytes. These can by Uploaded by a "U" 08H 00H followed by eight new pattern bytes. The Color codes from 49 throuth 63 are Uploaded by a "U" 78H 00H and the 120 bytes that define the 15 cell patterns. The Color codes from 64 through 127 are produced by a dither matrix. This is created by assigning elements of an eight by eight matrix the values 63 through 126. The matrix is Uploaded by a "U" 40H 00H followed by the 64 elements in row major order. PITFALLS AND LIMITATIONS This section amplifies the more subtle points and limitations of ZPLOT's commands. The valid range for coordinate values is 0 to 1. This corresponds to binary integer values from 0 to 32767. As each point is plotted, a check is made to insure that the coordinate is within the memory map. If it is not, the point is not plotted. This is mainly to keep the program from running amok and writing over parts of memory that are not part of the memory map of the picture. This is not intended to be a form of windowing. If you want to zoom in on a part of a larger picture, the picture should be clipped by the application program. Note also, that most high level languages will not deal with positive integers that are larger than 32767, as these larger numbers represent negative integers. In contrast to the coordinate values used for all of the graphic commands, any coordinate value outside the picture used to indicate the start of printing a string will be set to zero. This is intended to make the String command act as much as possible like a normal printer. When the string goes off of the right hand side of the plot, the X coordinate for the next character will be set to zero and the string will wrap around - just like a carriage return without a linefeed. All characters that attempt to be printed above or below the plot will be printed on the bottom line. String has a few other points of interest. Only printable characters should be used. Control characters and escape codes will occupy their respective positions in the memory map but will not be printed. This will cause the rest of the line to be shifted to the left and destroy its alignment with the rest of the page. Also, the character pitch must agree with the character width set at assembly time, or the alignment will be affected. The coordinates for the start of the string are truncated to the nearest multiple of the size of the character. Thus the specified point will be within the first character, but the character will not be centered or aligned with the given coordinate position. This was done because most printers insist that the printed characters occupy these locations, and ZPLOT has to respect this or the aligment of the rest of the line will again be affected. ZPLOT prints the strings, it does not plot them as line segments. Because of this, a printed character will absolutely occupy its location on the plot, and any overlapping lines or points will not appear. If a character is printed on a patterned background, it will appear as if it were in a white box the size of the character. If true graphic characters are desired, they must be drawn by the application program as line segments. An additional implication of the printed characters is is their size relative to the graphic bit images that are sent to the printer. The graphics are printed in "strokes" that are one dot wide and seven dots high. Many printed characters are higher than seven dots especially those that have descenders. A printed character occupies a space that is seven dots high in the memory map. Thus, the top line of capital letters and the lower case descenders can overlap the graphics area above and below the nominal area of a printed character. The distance that the paper is advanced between lines is dictated by the height of a graphic "stroke", and is nearly always smaller than the normal single spaced distance. Printed lines must therefore be "double spaced" by specifying starting coordinates that are well separated vertically. This is a device dependent aspect, and a litle experimentation may be needed to achieve a good appearance. The last caution about the String command is that it MUST end with a carriage return character. This signals the end of the string, and without it, the program will continue to read the rest of the input file as part of the string until it either encounters a carriage return or the end of the file. The String and Text commands are the only commands with this potential, as all of the others have a definite number of bytes of data. All these caveats regarding the String command may sound a little gruesome, but it is really not much different from normal printing. If its limitations are too inhibiting, you must draw the characters instead of printing them. The Text command is output to the printer at a different time than any of the other commands. Its contents are sent immediately when it is read, whereas all other commands cause their actions to be stored in the memory map and only printed when an Output command is received. Thus, it cannot be used to send escape sequences to the printer in the middle of the plot. Whether graphics commands (such as Draw, Fill, etc.) preceed or follow a Text command is immaterial, since these commands affect the memory map at the time that they are read and not the printer. What really matters is the position of a Text command relative to the Output commands in the file. Like the carriage return at the end of the String command, omitting the 0 byte at the end of the Text command can have disastrous consequences. The line spacing used in the Text command is different from the line spacing in the plot itself. The Output command sets the line spacing to be appropriate for graphics, and then resets it to the normal text single spacing when done. If a uniform appearance is required throughout, each Text command should contain the control characters or escape sequences required to set the line spacing to match that used in the plot itself. The final consequence of the line spacing is that the form length and the top of form position set in the printer will be wrong. The Output command will result in the printer being positioned at the bottom of the plot. This is to allow several plots to be printed sequentially as one continuous picture without any gaps between them. In order to advance to the top of the next page, the Text command must be used to issue the correct number of line feeds and then tell the printer to reset the top of form. The Output command does not erase the existing picture. Thus several copies of the same plot can be produced by repeating the command. In addition, this allows building up a picture in stages and printing it at each stage. To print one plot and start anew, you must Output the first, set the Color to white, Erase the page, and then set the Color back to the plotting color or pattern. The program does not automatically execute an Output command at the end-of-file or when Quitting. You must include an Output command to get any output at all. This philosophy is to accomodate those devices, like graphic terminals, that display the plot as it is being made, and only need an Output command for hardcopy. ERROR MESSAGES Disk is Full. Fatal error. No more room exists on the designated disk for writing the output file. Ensure that enough room is available and run ZPLOT again. Note that a different drive/user/directory may be specified for the output file than the one used for the input file (when running under ZCPR3). If disk space is not available, run ZPLOT in the direct printing mode. Any remnant of the output file may be printed, but the last record will probably contain an incomplete graphic output sequence. The printer will expect to receive additional bytes of graphics. This will produce a swath of dots with a random apperance, unless nulls are sent. In addition, the printer line spacing will remain set for the size of the graphic output. End of File. Fatal error. The end of the input file was encountered when ZPLOT attempted to read the next record. Add a Quit command for the normal termination of the program. File not Found. Fatal error. The file name given for the input file could not be found on the disk. Make sure that the spelling was correct, that the proper drive is specified in the file name, or the right drive is logged in as the default drive. No Directory Space Available. xFatal error. When ZPLOT tried to make a new output file, there was no more room in the disk directory. Erase a file, use a different diskette, or run ZPLOT in the direct printing mode, without making an output file. No File Specified. Fatal error. No input file name was given. ZPLOT will not prompt you for a file name, and there is no interactive mode for entering commands. Create an input file and try again. Undefined Command Character Encountered. Warning error. When ZPLOT attempted to interpret the ASCII letter portion of a command, a character was found which did not correspond to one of the established commands. ZPLOT ignores these characters and attempts to interpret the next character as a command. If a command does not have the proper number of data bytes, or if an extraneous character is inserted in the middle of the data portion of a command, the rest of the file will be out of sequence. Eventually, ZPLOT should get back in step with the command stream, but the overall effects are unpredictable. INSTALLATION INSTRUCTIONS SIZING THE MEMORY MAP ZPLOT has been designed to keep the printer driver program small while providing the necessary primitive graphic operations for producing most pictures and plots. The reason for the simplicity of the of the command set is because the bit map for the picture is LARGE. It can use as much memory as your computer can give it. The size of the memory available for the bit-map, in conjunction with the resoultion of your printer, sets the size of the plot that can be made. The first step in installing the program is to decide how large the memory area for the bit map can be. The program itself occupies about 4K. Subtract this from the size of the TPA, and reduce the result by a little more to provide a conservative pad. The end result is the target size for the size of the memory map. Divide the target size by the printer resolution (dots per inch) in the horizontal direction, and divide again by the printer's vertical resolution. Multiply this result by 7 (7 dots are stored in each byte). You now have the number of square inches that can be plotted. Take the square root, and round down to a convenient size for each side of the plot. Now multiply the height of the plot by the printer's vertical resolution and round down to the nearest multiple of 7. The number of dots in the vertical direction should be a multiple of 7 because seven dots are stored in each byte of the memory map. ZPLOT has no provisions for handling a byte which is contains bits that are part in and part out of the map. You now have the total number of dots in the vertical direction, and dividing by 7 gives the number of lines that will be printed when the plot is made. Finally, divide the number of dots in the vertical direction by the vertical resolution to get the final size, in inches, of the plot. Multiply the final size of the plot by the horizontal resolution to get the final number of dots accross the page. The final map size is the product of the number of dots horizontally multiplied by the number of dots vertically, divided by 7. As an example, consider a 56K system. Subtracting 4K for the PLOT program and 100H for the start of the TPA: Target Size = 57344 - 4096 - 256 = 52992 bytes The Epson MX-80 has 60 dots per inch horizontal and 72 dots per inch vertical resolution. Target Size/HRes/VRes*7=52992/60/72*7=85.9 sq.in ==> 9.2 in. per side Since the MX-80 can only plot 8 inches horizontally, the plot is limited by the physical limits of the printer, not by the memory avalilable. Calculating the vertical number of dots for an 8 inch plot: 8*72=576 dots ==> 82 lines @ 7 dots/line ==> 574 dots vertically Since only 2 dots were lost due to truncating to the nearest number of whole bytes, there is little point in trying to adjust the horizontal size to keep the plot square. The horizontal size is therefore: 8*60=480 dots The final map size is calculated as: 480*574/7=39360 This is the default size to which the program is set, and if satisfactory, can be used as is. Virtually all Epson-compatible printers will accept this setting. PRINTER SETTINGS Once the plot has been sized, you are ready to modify the settings in the assembly language source file (ZPLOT.Z80), if you require a setting other than the default. The relevant equates are near the beginning of the program. MAPSIZE should be set to the value calculated above. MAXX and MAXY must be set to 1 less than the number of dots in the horizontal and vertical directions. For the example above, MAPSIZE becomes 39360, MAXX is set to 479, and MAXY to 573. Once the settings are made for your printer, assemble the program using ZAS or another Z80 assembler. DIFFERENCES BETWEEN ZPLOT AND PLOT33 Functionally there are none. Every valid PLOT33 command is a valid ZPLOT command and operates identically. However when ZPLOT is operated under ZCPR3, it will recognize DU: or DIR: specifications in input or output files. The code has been extensively changed to make full use of the Z80 instruction set. All the registers are used (if your BIOS trashes IY, then ZPLOT won't work!). Despite the extra features, the code is about 1/2K smaller. Since virtually all dot-matrix printers today accept the Epson graphics commands, all the conditionals in the source code for non-Epson printers has been removed, making the source just editable by ZDE (if you have 60k tpa) FUTURE ENHANCEMENTS Zplot was intended to be a first step to a permanently resident plotting utility, living in banked memory that could be called by a BDOS call by any applications program. At the moment, there is no agreed method of handling memory over 64k in a portable manner, though writing the code so to do is not difficult. I had originally started writing a utility based on HP-GL plotter commands, then I discovered PLOT33, by Tom Speer, and decided the command set was much more elegant than the HP commands. So the first step was to translate PLOT33 into Z80, optimize it for that CPU, and add ZCPR3 support. The result is ZPLOT. One big improvement possible would be to use the Z280 multiply and divide instructions. This program is very multiplication and division intensive and would really benefit by having a Z280. Next, the error messages should be loaded into the Z3 message buffers instead of simply being displayed. With an appropriate error handler enabled, ZPLOT should be able to operate very robustly inside aliases.