Print about printers. (evaluation of plotters with drum mechanisms) (column) David H. Ahl.

This month, Print about Printers should perhaps be retitled, "Plots About Plotters." All of the plotters we have evaluated to date have been flat bed units. Thus, we were interested in the Strobe plotter which uses a drum mechanism and the Laser unit which uses a roller (or small drum). The Strobe units are full-function plotters selling in the near $1000 range while the Laser PP-40 at $199 is one of the least expensive plotters available. Strobe Model 260 Plotter The Strobe Model 260 is an eight-pen drum plotter designed for use with a wide variety of microcomputers. Strobe also manufactures two one-pen plotters, the Model 100 and Model 200. Most of this review will apply to all three plotters.

The 200 series of plotters uses 8-1/2" x 11" paper and has a plotting area of 8" x 10-3/4". Accuracy and step size are both 0.002" (or 0.05 mm). As a result of the drum design, the plotter is a relatively compact 16.8" x 10.3" x 4.1".

In addition to its primary function as a plotter, the unit can be used as a digitizer (reading points) as well. Setting Up

As it comes out of the box, the 260 is one of the most complete packages we have seen. The carton includes the plotter itself, pen assembly, manual, and packet of 50 sheets of paper. As we had ordered the Apple version, also included was an interface card and six-foot connecting cable.

The plotter is easy to install: just plug in the power cord and RS-232 interface cable, set the baud rate and parity switches, and you are ready to go. Or so we thought. Although we had ordered the Apple card, we first tried the plotter with a NEC 8201, the computer we have used for our previous three plotter evaluations.

We connected the computer to the plotter with a reversed RS-232 cable (2 to 3, 4 to 5, 6 to 20, etc.) as described in the manual. Incidentally, the description of this interface in the Strobe manual is one of the best we have ever seen. Indeed, the manual has one of the only clear descriptions around of the various methods of software handshaking (Xon-Xoff and Enquire/Acknowledge).

Unfortunately, the manual was of little help when the plotter head moved just a tad and then refused to do anything else. After three hours of experimentation with baud rates, parity, reversing connections, new cables, and the like, we gave up and hooked it up to the Apple. Same problem.

So we called Strobe and a helpful customer service person, Dave Golden, talked us through a setup procedure. Still, no go. In desperation, we took the cover off and reseated all the chips and connectors. Lo and behold, upon power up, it worked fine. Lesson: even with the best packaging, shipping can be rough on delicate electronic equipment.

Incidentally, the parity slide switch is neither labeled nor described in the manual. For the information of future Strobe customers, up is even parity, center is none, and down is odd.

Paper loading on a drum plotter is somewhat more awkward than on a flat bed unit, although with a bit of practice it becomes easier. The plotter uses standard letter-size paper; however, Strobe recommends paper with a smooth, non-porous surface. This commonly known as coated stock and is similar to the stock on which most magazines are printed. Ink takes longer to dry on this type of paper, so you must be careful not to touch a finished plot for a minute or two after the last line is drawn.

The one-color plotterrs can accept several commercial pens such as the Pilot Razor Point or Spree Roller pen. The Model 260 comess with an eight-pen assembly which must be obtained directly from Strobe. Unfortunately, the manual is written for the Model 200 and the section of Pen Loading gives no clue as to how to load the eight-pen assembly. Back on page 4-20, with the description of the Select Pen command, a diagram shows the pen assembly. From this, we deduced that the assembly should be loaded with the black pen pointing toward the plotter drum. Controls And Buttons

On the top of the plotter are a red LED power indicator, two rocker switches, and six buttons. The switches select whether the plotter is on or off line and the pen position (up or down). The buttons move the pen manually in any of four directions or to the home position. One button, marked Start/Enter is used to designate manually the point at which the pen is initialized.

For normal plotting, most of these manual controls will not be used, but they are handy in case you want to put several small plots on the same sheet of paper (although this, too, can be done in software rather easily). These controls, of course, are necessary for using the unit as a digitizer. Plotter Commands

Commands are sent to the plotter as you would send them to any RS-232 device. Although the commands are described in detail in the manual, a major shortcoming is the total absence of examples. Moreoever, the Apple demo program is in machine language, which is of no help if you are trying to figure out which of the following statements to use to move the pen: PRINT #1,PA 1000,1000,0,1000; PRINT #1, "PA" 1000,1000,0,1000; or PRINT #1, "PA 1000,1000,0,1000;"

The commands fall into three major groups; communications, device control, and graphics plotting. The communications commands are used to set the handshake mode (one hardware and three software modes), turn the plotter on and off, reset the plotter, and read the amount of buffer space remaining. The plotter has a 512-byte buffer which you normally won't have to worry about. However, if you like to be in control of absolutely everything, you can bypass the normal handshaking and devise your own approach with the buffer commands.

There are 25 graphics instructions which provide the means to raise and lower the pen, change pen colors, draw alphanumeric strings and plotter symbols, and create graphics.

A plot unit is 0.002" which means that the plot dimensions on a standard sheet of paper are 5375 by 4000. There is no provision for automatic scaling, so all scaling must be done in user programs. Within this grid, the pen may be moved to an absolute location (PA) or moved relative to its previous position (PR).

Upon startup, the plotter is automatically initialized; however, this command can be given through software as well. The Home Pen command moves the pen to he home position, a good practice at the end of a plot. For positioning a plot on a sheet of paper, the origin can be defined at any point with the DO (Define Origin) command.

The plotter has four alphabetic character sets for various foreign languages. Each set has 96 plotting characters. In addition, there are nine symbols (diamond, triangle, x in square, etc.) that can be used on line graphs (or anywhere you wish).

The basic character size is 0.016" high by 0.008" wide (mighty small), but characters are generally drawn as multiples of this basic size. The default multiple is 8, which is slightly larger than standard 10-pitch pica type. A multiple of about 600 will produce a character that fills an entire page. We found the characters were very legible from size 3 on up.

Characters can be drawn in any of four directions. Figure 1 shows the upper case alphabet in two directions in character size 10. Making Plots

Once we got the hang of it, the Strobe was easy to use. A nice feature with the Apple version is the included Apple Starter disk which contains six sample plots and chartinga routines. The plotter has a self-test (hold down Start/Enter upon power up) not mentioned in the manual, and the plots on the Apple disk are a good test, too--perhaps too good.

On multiple color plotters, a frequent problem is pen alignment. The Strobe is no exception. Figure 2 shows five short line segments drawn with five different pens. Yes, they are within the specified 0.002",. but just barely. We would not call this a straight line.

Figure 3 uses four colors and is very effective on a bar chart of this kind. Since the chart communicates its message, it is less evident that the bars actually go below the bottom x axis or that the top portions of the bars are slightly out of alignment with the bottom portions. Indeed, multiple colors on an inexpensive plotter have a cost in precision.

The plotter uses a system of precisely notched rubber belts, plastic gears, and servo motors to position the drum, pen head, and pen turret (change colors). If the plotter is attempting to execute several commands in rapid succession, it occasionally does not rotate the pen turret to a full stop. Figures 4a and 4b show the same pie chart, but in 4b, the pen turret did not rotate fully to the black pen, so two pens actually made contact with the paper producing an interesting, but unwanted effect.

Basically, we feel that multiple colors are very nice, but are best used in places where precise matching of lines and boundaries is not critical. For example, the line graph in Figure 5 uses color effectively, and mismatches are not evident. As a Digitizer

In digitizer mode, you fasten the diagram or chart you want to measure to the drum and give the plotter the DP digitizing command. In this mode, the pen is used as a cursor and may be moved with the four directional buttons to any point on the plotting area. When the Enter button is pressed, the current coordinates are saved and can be accessed by the computer with the OD (Output Digitized Point) instruction. The coordinates are given in absolute plot units (0.002").

The manual describes how to use the digitizer mode in conjunction with the plotting mode, and presumably this would be valuable for some engineering applications. Frankly, we are not familiar enough with these applications to give them a real workout. We tried the digitizer mode and it worked, although it is very difficult to position the pen accurately when it is in the up position. (this is true with any plotter, not just the Strobe.) Documentation

The user's manual has three sections: a 16-page introductory section with specifications and set up instructionse, a 1 6-page section describing the starter disk, and a 64-page section describing communications and the graphics commands.

The introductory, starter disk, and communications sections are excellent. Indeed, as we mentioned earlier, the section on communications is the best we have ever seen.

The section on the graphics commands is adequate in its description of the instruction but totally devoid of examples. This we regard as a major flaw. We think a plotter manual should have examples of its commands for several computers and should have portions of plots to show that these commands actually do. The Last Line The generalized routines on the Apple Starter Disk (available for the IBM PC and CP/M machines as well) are excellent for producign bar, pie, and line graphs. However, if you want to go beyond that, you must commit yourselft to spending some hours of experimentation determining how the commands work with your computer, and how to produce the plots you want. Although the various colors do not line up precisely, we feel that they can be use to produce acceptable and very effective charts for business and personal use. For architectural and engineering drawings and precise mathematical plots, we feel it is best to stick to one color.

For under $1000, the Strobe Model 260 eight-color plotter ($995) and the even less expensive ($695) Model 200 one-color unit offer good value for producing letter-size plots. The included software disk is a nice extra, and it is reassuring to knw that Strobe maintains a responsive customer service department too.

For more information, contract Strobe Inc., 897-5A Independence Ave., Mountain View, CA 94043. (415) 969-5130. Laser PP40 Printer/Plotter The Laser PP40 is an inexpensive ($199) four-clor printer/plotter from Video Technology. It has a Centronics parallel interface so it is suitable for use with a wide range of computers, not just the machines from Video Technology. It uses 4-1/2" wide roll paper, so it is not suitable for low-cost plotting it is an excellent unit.

The PP40 is one of the smallest printer/plotters we have seen, measuring a diminutive 9.5" x 4.5" x 2.1". Anexternal 8-volt, 1500 ma power supply is also furnished. On the outside of the case we find a rocker off/on switch, red LED power indicator, and three press switches for paper feed, pen change, and color change. On the back are connectors for the power input and Centronics-type interface cable.

To connect the PP40, you will need a cable from your computer with a centronics-type connector. Some computers such as the Laser 200, Vic-20, TI 99/4A, and Timex/Sinclair 1000 require a separate interface, while on higher-end u nits this interface is built in. paper loading is very simple, as are pen mounting and pen changing. The PP40 comes with one roll of paper and four pens with the fine ball tips (black, red, green, and blue). Additional paper rolls are available from office supply dealers, while replacement pens must be purchased directly from V-Tech. Although it is not mentioned in the manual, we suggest removing the pens from the unit and replacing their covers in you plan to let the PP40 stand idle for more than a day or so.

On the bottom of the unit is a small plate that covers a DIP switch. One switch selects whether carriage return implies line feed for not, and the other selects 40- or 80-column priting (spelled on the box, "coloum"). Forty-column printing produces 11 characters per inch and 5.5 lines per inch. Eighty-column printing uses a much smaller character size, and produces twice the vertical and horizontal density (22 cpi and 11 lpi). See Figure 9. Using this character size (0), the print speed is 10 cps; the larger the character, the slower the print speed.

The PP40 has a character set of 95 ASCII characters (see Figure 6).

In the 40-column printing mode, characters are produced in size 1. In the graphics mode, the PP40 can produce 64 character sizes; the second size si shown in Figure 7, and sizes 0 to 20 are shown in Figure 8. Size 63 is very large indeed with each letter measuring 2" x 3". Graphics Mode

In the graphics mode, the PP40 can produce plots 96mm (3.7") wide in the x direction by 6.55 meters (over 21 feet!) long in the y direction. The x direction is divided into 480 steps each 0.2mm in size; the y direction can have up to 32,768 steps. In reality, however, you will probably use on a fraction of the y direction potential. Resolution with any color pen is 0.2mm, and drawing speed is 52mm per second.

The graphics commands recognized by the PP40 are nearly as rich and varied as those on much larger and more expensive plotters. The PP40 can produce 15 different types of dotted lines, as well as a solid line. It can also produce coordinate axes automatically.

The draw command (D) draws a line between any number of x, y point pairs, while relative draw (J) draws a line from the present location to an X, y point pair. Move and relative move function similarly, but with the pen up.

The color command (C) selects a pen color, scale set selects one of 64 character sizes, and alpha rotate selects one of four directions for the printing of alphanumerica characters.

The CC40 has three initialization commands: A intializes everything and puts the plotter in text mode; I causes the present pen position to be taken as the starting point; and H moves the pen to the home position with the pen up.

The only bone we have to pick is that the plotter requires that commands and separators (commas) be sent to the plotter enclosed in quotation marks in an LPRINT statement. Most other modern plotters do not require quotes. For example, a draw command between three point pairs must be sent to the PP40 as:

80 LPRINT "D"; X1;", ";Y1;", "; X2;", ";Y2;",0,0"

On other plotters, this line would read:

80 LPRINT "D" X1, Y1 X2,Y2 0,0

As might be expected, the PP40 does not draw true diagonal lines. Instead, these lines are produced as a series of horizontal or vertical straight lines with small steps to creat the diagonal direction. These steps are evident in the spiral plot shown in Figure 9. Documentation

The user manual for the PP40 is better than many of the manuals that come with many other Hong Kong products, but it is still nothing to brag about. All the graphics commands are described in a condensed half-page table. Fortunately, the second half of the 38-page manual is devoted to six example plots. Program listing are provided for three computers: Laser/V-Tech 200 (standard Microsoft Basic), Apple II (Applesoft Basic, and Dragon 32 (same as Radio Shack Color Computer). By studying these programs, you should be able to determine how each text and graphics command functions. The Bottom Line

Frankly, we like the PP40. It is not a professional, full-function plotter, nor does it take the place of a full-size printer. However, as an inexpensive output device that can do both printing and plotting, it does an admirable job.

The graphics command structure is somewhat cumbersome; diagonal lines are not truly straight; and the documentation could be improved upon. Nevertheless, t hese are small inconveniences against the good performance, compact size, and low ($199) cost of the PP40.

For more information, contract Video Technology, 2633 Greenleaf Ave., Elk Grove Village, IL 60007. (312) 640-1776.

Products: Strobe Model 260 plotter (computer apparatus)
Video Technology Laser PP40 (computer apparatus)