Plots about plotters. (evaluation) David H. Ahl.
Since this issue of Creative Computing is devoted largely to graphics, it seemed appropriate for our Print About Printers column to become Plots About Plotters.
We performed in-depth evaluations of two plotters, an eight-pen unit from Roland, and a single-pen unit from Enter Computer. The Roland unit is very similar to their one-pen plotter and our comments apply to both units. Enter Computer recently introduced a six-pen plotter; we have included it in the chart and have some comments about it, but we did not do a hands-on evaluation.
Of the many plotters we have evaluated over the years, seven are still the current models. Question to readers: would you like a roundup of these and all other currently available plotters in a future issue? More than just specifications, this would include our impressions and, in two cases, results from long-term use (sort of a 24,000-mile evaluation). Roland X-Y Plotters
Roland DG Corp. manufacturers two plotters, the DXY-800 (eight pens) and DXY-101 (one pen), specifically for use with microcomputers. Unique among small plotters, the units can be used in either a horizontal or vertical position. We tested the DXY-800; however, most of our comments apply to both units. Out of the Box
Packed with the plotter are eight colored pens, four pen holders (for standard nylon-tip pens), a stand (to hold the plotter in a vertical position), a power supply, and a manual. The only thing not included are an interface cable and paper.
The plotter measures 17" x 19.5" x 3"; an external power supply has two cables, one to the plotter and one to the outlet. In the horizontal position, the plotter occupies 16" x 20" of desk space; using the heavy wire stand to put the plotter in a vertical position, the footprint shrinks to 10" x 20".
The largest paper accepted is 420 x 297mm (apparently a standard European size). The corresponding U.S. dimensions are 16.5" x 11.7"; the nearest standard size in the U.S. is 17" x 11".
Although the manual seems to suggests that plots can be drawn on the entire 420 x 297mm surface of the paper, this is not the case. The maximum area for plotting is 350 x 260mm (approx. 13.8" x 10.2"). The DXY-101 has a maximum x dimension of 370mm (14.6").
Two convenient magnetic strips hold the paper in place on the right and left. For large plots we would have appreciated additional strips for the top and bottom. These are available as extra cost options, although we found that masking tape worked just fine.
On the back of the plotter (assuming horizontal placement) are several connectors and switches. The plotter can accept input through a parallel (Centronics) or serial RS-232 port. For serial operation, DIP switches are used to select the baud rate, parity, data bits, and stop bits. We tried both interfaces and had no problems with either one.
A push button off/on power switch is found on the back. In addition, at the top right of the plotter bed are two other switches (Pen Up/Pen Down and Home) and two LEDs (Power On and Pen Up).
Eight pen holders are at the top left of the plotter bed. Each one holds a Roland pen or a standard pen holder. We tried a Pilot Razor Point pen with good results, although we can't see any reason not to use the included pens. Included colors are black, red, blue, green, pink, orange, purple, and brown.
Plotting is accomplished by means of a vertical bar which moves from right to left with a pen holder that moves up and down along the bar. Step size is 0.1mm (0.004") and repetitive accuracy is 0.3mm (0.012"); in actual use, we found the plotter performed well within this limit, even with pen changes to other colors.
Like other plotters, the DXY-800 is fairly noisy in operation, particularly when making a series of small steps or pen up/pen down movements. Drawing Commands
The plotter recognzes 20 commands. All commands are a single letter, although all but one require one or more arguments. Home (H) is the only single letter command; it moves the pen to the 0.0 position.
Two commands, Draw (pen down) and Move (pen up), cause the pen to move to a position specified by x-y coordinates. As there is no scaling, these coordinates must be specified in integers representing 0.1mm (max. 3500 x 2600).
The Increment command draws an incremental distance from the last pen position; the Relative command performs the same operation with the pen up.
The Line command draws solid or dashed lines with variable spacing. The Axis command draws hash marks along an x or y axis.
A group of four commands is used to draw alphanumeric characters and ten graph symbols in any of 15 different sizes (0.7 to 11.2mm high) and four directions (0, 90, 180, 270 degrees).
A group of four commands is used to draw circles and arcs in either absolute or relative locations. Arc angles are specified in degrees rather than radians--a welcome feature. On the other hand, these commands can draw only circles (or portions) and not ellipses (which are possible on some other plotters). A related command is "K" which draws division lines (like hash marks) in a circular pattern.
Finally, the "T" command draws hatching (series of slanted lines for shading enclosed areas) within any defined rectangular area.
This is a comprehensive command set, although compared to a plotter such as the Houston Instruments DMP-29, the Roland DXY units are "missing" several useful commands. Lacking, for example, are commands to reset the plotter, draw ellipses, draw different types of lines (other than solid and dashed), do scaling, change the pen speed, change the step size, and connect points of an irregular curve. Even without these commands, the Roland plotters are quite versatile; nevertheless, certain types of plots will require more programming than they would using a plotter with more built-in "intelligence." Documentation
The Roland plotter comes with a 31-page manual which we rank as adequate--no more, no less. As far as interfacing, if you are connecting the plotter to an Apple, TRS-80, or IBM PC with standard parallel interface, the instructions are complete. (Actually, they are fine for a parallel connection to any computer, although only the above three are mentioned.) If you plan to use a serial interface, the manual provides the necessary information, although it is quite technical. IBM PC and Apple cable connections are given, but no others.
Seven pages of the manual are developed to a short description of each command along with a short program listing and a sample plot. Our applause to Roland for including this detail, something sadly lacking in the documentation of nearly every other plotter we have evaluated.
One-half a page is devoted to describing the printer mode (using the plotter to print text); we found it inadequate. We also felt that the single page devoted to error indication and recovery could have been expanded. Good Price Performance
While the Roland DXY-800 does not have all the features of some other plotters, neither is it as expensive. Indeed, in the under $1000 price range, the DXY-800 is one of the few plotters able to handle 11" x 17" paper and eight pens. The pen holders for standard pens are a nice plus as are the built-in parallel and serial interfaces. Furthermore, with the upright stand, it has the smallest footprint of any unit that can handle 11" x 17" paper. We can't attest to its longevity, although it appears to be ruggedly built. The bottom line: for under $1000, the Roland DXY-800 is an excellent buy.
For business graphics, Roland offers a comprehensive software package which automatically produces line, bar, and pie charts according to your specifications. Furthermore, it has the capability to read files from popular spreadsheet packages and graph the data. This package sells for $375. When it was first introduced in April, Roland offered an attractive package price which included both the plotter and software; you might want to ask your dealer if this is still available. Sweet-P Model 100
The Sweet-P Model 100 "Personal Plotter" by Enter Co mputer Inc. is one of the smallest units on the market. It achieves its compactness by means of a novel plotting mechanism that moves the paper back and forth on precision rollers while moving the pen from side to side. As a result, it occupies only 14" x 9" of desk space, but can produce plots on 8-1/2 x 11" paper. Complete As It Comes
The Sweet-P plotter comes complete with everything needed for immediate operation: manual, 12 colored pens, interface cable, packet of paper, and disk of software (for Apple or IBM PC). Although the plotter is supplied with either Apple or IBM PC cable and software, it will work with any computer. In some cases you may have to use a different cable. The plotteer comes with a parallel interface only.
Hint: the Apple cable will work with TRS-80 Model 100 and NEC 8201 notebook portables while the IBM cable will work with any computer with a DB-29 connector (RS-232 type) on the parallel output port. It would have been useful if Enter had made available a cable for the plotter with a standard Centronics connector for use with the many computers that have this connector.
As mentioned, the plotter is very compact. In operation, however, you must provide sufficient space in the front (5") and rear (6") for the paper to slide back and forth.
Under normal circumstances, most users will use 8-1/2" x 11" paper. However, the mechanism is such that it can accommodate roll or fanfold paper (8-1/2" wide). Active plot dimensions, no matter what length paper is being used, are 7.35" x 10". Step size is 0.004" and there are 2500 steps in the X direction and 1838 steps in the Y direction.
The paper is held in place by two rubber rollers at either end of the platen. We found the mechanism was equally adept at handling 50# coated stock, projector transparencies, and light layout board.
A rocker power switch is found on the left rear of the unit while a small green LED at the left front indicates when the plotter is on. On a sloping surface at the right are 12 touch sensitive switches. Nine of these switches control pen position and movement: pen up and down, move to upper right or lower left, move in one of the four directions, and accelerate pen speed. PAUSE suspends plotting activity and moves the paper out to full view position; pens may changed at this time. SELF TEST runs a test plot, and PEN DELAY causes a pen drop delay required by some commercial pens.
Four pens are furnished in one packet (black, red, blue, and green), and eight more (no duplicate colors) are in the support pack which also includes 100 sheets of smooth finish paper.
In operation, the paper moves back and forth, and the pen from side to side. Step size, distance accuracy, and repetitive accuracy are all 0.004". Default pen speed is 5.7" per second, close to the maximum of 6"/sec. For certain types of plots, a slower speed is preferable; the Sweet-P has 16 speeds from 1.4"/sec. to 6"/sec. Making a Plot
As mentioned above, the Sweet-P plots points from 0 to 2500 in the X direction and from 0 to 1838 in the Y direction. Points can vary between -32,768 and +32,768 without causing errors which, in the case of plotting certain mathematical functions, simplifies the programming somewhat.
Commands are issued to the plotter in LPRINT statements. The plotter recognizes 19 commands, all of which consist of two letters; 15 require one or more arguments.
Basic plotting is done with the Draw (pen down) and Move (pen up) commands. These commands can specify an absolute x,y location or a location relative to the last pen position. A related command is Line which draws one or more lines between series of coordinates. Another related command is Point which moves the pen from its current position to a specified coordinate and makes a point mark.
Three commands control the pen: Pen Up, Pen Down, and Velocity (sets the pen speed).
The Reset command reinitializes the plotter and causes all settings to return to their default values. Home returns the pen to the home (0,0) position. Page Length sets the page length to any value between 1" and 121"; the default value is 11".
The Text command draws alphanumeric characters (numbers, letters, symbols) starting at the current pen position. The normal text delimiter (marks beginning and end of text) is a semicolon; this delimiter can be changed with the Text Delimiter command. Text can be drawn in any of 255 sizes from 0.08" high to 20.4" high and in any of the four directions (0, 90, 180, 270 degrees). We can't see too much use for very large characters, particularly since they won't even fit on the paper.
The Mark command draws a specified character centered around the current pen position. This is useful to define points on a graph although, unlike many other plotters, there is no special set of graph symbols, only the standard ASCII symbols.
Two commands, Axis X and Axis Y, draw lines along the positive X or Y axis with hash marks spaced at specified intervals.
This set of commands includes several not found on other plotters; conversely, the Sweet-P lacks some commands found on other units. Most notable of the "missing" commands are those to draw circles, ellipses, and arcs; connect the points of an irregular curve; draw dashed and dotted lines; do hatching or shading; and perform automatic scaling. All of these things can be done by programming, although calculating circles and arcs can be quite cumbersome and messy.
Making up for the lack of these commands for some applications is the included disk of software (Apple or IBM PC and compatibles). this disk includes five demonstration programs, useful mainly for looking at the programming involved to produce the sample plots. Also on the disk are three graphing programs to produce line, bar, and pie charts automatically. There is also biorhythm rpogram and a tutorial which repeats the programming examples in the manual. Documentation
The 48-page Operator's Manual is divided into nine sections, five of which consist of just a page or two. The first long section describes unpacking, connecting, and setting up the plotter. It is well-illustrated with photos and diagrams and leaves nothing to the imagination.
A thorough description of the commands, complete with many sample programs and plots, is included in a 22-page section--one of the best we have ever seen. A similarly comprehensive section describes the contents and use of the demonstration/programming disk.
The shorter sections cover troubleshooting, maintenance, specifications, and warranty. A two-page Quick Reference Guide gives a summary of the plotter commands, conversion table (plotter units, inches, millimeters), and default settings. Meeting Your Needs
We feel the Sweet-P Model 100 will meet the demands of the majority of people for basic business graphics. The plotter is less suitable for mathematics and engineering applications because of the 8-1/2" x 11" paper size and the lack of circle/arc commands. Its remarkable compactness means it can be easily carried around; it fits nicely in an attache case.
Enhancing the suitability of the Sweet-P for business applications is the Presentation Package, a $90 kit which includes 25 pieces of transparency film 25 frames, and two sets of four colored transparency pens.
In addition to the software disk included, several third party software publishers produce software that can take advantage of the Sweet-P features. Couple all of these factors with its modest $795 price tag, and the Sweet-P Model 100 definitely goes on our recommended list. A New Entry From Enter
One step up from the Sweet-P Model 100 is the new Six-Shooter Model 600 plotter from Enter Computer. We did not test this plotter; However, its specifications look most impressive.
It has both parallel and serial interfaces, and a six-pen rotary penholder, and can handle 11" x 17" paper. It has an impressive list of 54 commands including ones for automatic scaling, drawing arcs and circles, shading rectangles and wedges, and selecting alternative character sets (19 of which are built in). In addition to responding to these commands (called the Sweet-P Graphics Language), the Six-Shooter also responds to the instructions for the Hewlett Packard 7470 and several other HP plotters. As a result, there should be a fair amount of third party software immediately available for this unit.
Moreover, an additional 12 commands allow the unit to be used as a digitizer. At just $1095, the Six-Shooter certainly warrants your careful consideration.
Products: Roland X-Y Plotters (computer apparatus)
Sweet-P Model 100 (computer apparatus)