Chapter 14

DEC­writer III/​DEC­printer III (LA120)

Overview

The DECwriter III and DECprinter III are serial, dot-matrix, pedestal-mounted printers that combine bidirectional printing and a 1K character buffer to achieve 180 character-per-second throughput. The printhead automatically seeks the next print position, skipping over large areas of white space. With over 200,000 DECwriter III and DECprinter III printers already sold, these products have achieved a solid reputation for continued reliability.

The DECwriter III, the keyboard send/receive version, was specifically designed to be easy to use. It guides you through the wide range of available configuration choices, uses mnemonic commands, has a prompting LED display, and a special decal that summarizes set-up commands, and comes with a convenient pocket-sized operator card that explains procedures for selecting features.

Utilizes the proven technology of its keyboard send/receive (KSR) partner, the receive-only DECprinter III delivers high performance for local printing or communications. The DECprinter III incorporates an internal Function Control Panel, a series of controls and indicators, that permits rapid set-up, permanent or temporary storage, and modification of all necessary parameters. In addition to providing complete set-up control, the Function Control Panel displays the status condition of the terminal while in the set-up mode. An external operator panel provides for the selection of local mode, self-test, and top-of-form operation.

The following versions of the LA120 are available:

• LA120-DA: DECwriter III keyboard send/receive printer
• LA120-RA: DECprinter III receive-only printer
• LA120-RB: DECprinter III receive-only printer for four- to nine-part forms.

Major Features

The major features of the DECwriter III and DECprinter III printers are:

• 180-character-per-second bidirectional printing – for fast throughput.
• 1,000 character-line buffer – Enables the printer to accept characters faster than it can print them and to look ahead to find the shortest path to the next print position. This eliminates the need for fill characters when operating at 1,200 bits per second and improves throughput and utilizes the communication line efficiently. There is an optional 4K buffer.
• Selectable baud rates – Offers 14 data rates from 50 to 9600 baud plus eight split baud rates with five different half- and full-duplex modes for versatility in meeting communications requirements.
• Full and half-duplex modem support – Allows the printer to be connected to a modem or acoustic coupler, for compatibility with the dial-up telephone network.
• Adjustable margins, tabs, and forms settings – Top, bottom, left and right margins as well as horizontal and vertical tabs are easily adjustable and the set-up commands can be held in nonvolatile memory.
• Multipart form capability – The LA120 prints on six-part forms and a special model has been developed that prints on nine-part forms.
• Selectable character pitches – With eight different horizontal pitches and six different line spacings to choose from, the LA120 provides flexible printed output. Also, the expanded pitch can be used for labels and messages, while the condensed pitch saves paper.
• Optional character sets – National character sets include Finland, Denmark, Sweden, Germany, Norway, and France. In addition, the APL set is available as an option.
• Nonvolatile memory – Stores feature settings so they can be recalled at any time. There is no need to set up the operating parameters every time the terminal is turned on.
• Universal power supply – Lets you select the voltage setting that’s right for your environment.

Printing features

The DECwriter III and DECprinter III offer a seven-by-seven dot-matrix character cell that provides output at the rate of 180 characters per second. This is suitable for draft and data printing. Printing is done through a bidirectional technique in which the printhead seeks the shortest distance to the next printable character, rapidly skipping over blank spaces.

Character Sets

The DECwriter III and DECprinter III offer the full 94-printing-character ASCII set, and print both uppercase and lowercase characters. Optional international character sets include Finnish, Danish, Swedish, German, Norwegian, and French. In addition, the APL set is available as an option.

The LA120 printers can print double-width characters and compressed characters. Character sizes range from 10, 12, 13.2, and 16.5 characters per inch. Double-width characters print at 5, 6, 6.6, and 8.25 characters per inch.

Paper

The LA120 printers accommodate fanfold paper from 7.6 to 37.8 centimeters (3 to 14 7/8 inches) in width. Because the DECwriter III and DECprinter III printers have forms handling capabilities, they can format output to fit preprinted forms, up to six parts. The LA120-RB has been developed to handle four- to nine-part forms. It is not recommended for single sheets. Both the KSR and RO models can accommodate selectable form lengths up to 35 centimeters (14 inches).

Options

Accessories and Supplies

The following accessories, supplies, components, and spares are available for the DECwriter III and DECprinter III. Check with your sales representative or Digital’s Installed-Base Group for the latest information.

Supplies

Accessories

Operator Features

Indicators

The DECwriter III’s operator console displays eight indicator lights, while the internal Function Control Panel of the DECprinter III displays five indicators.

By raising the top cover panel of the DECprinter III, you can easily access the internal Function Control Panel. This panel permits rapid set-up, permanent or temporary storage, and modification of all necessary parameters. Besides providing complete set-up control, the Function Control Panel displays the status condition of the printer while in the set-up mode. An external Operator Panel lets you select local mode, self-test, and top of form operation.

The absence of a full keyboard prevents interference by personnel who may be unaware that their manipulation of the keyboard may be changing your set-up parameters and accessing the computer.

Voltage Selector/Power Switches

The DECwriter III and DECprinter III have a voltage selector switch so you can choose the right voltage. To select the appropriate voltage, place the tip of a pen into the switch indentation, as shown in Figure 14-4. Note: Do not use a pencil to change the switch.

The Power on/off switch is located below the voltage selector switch.

Set-Up

The DECwriter III has an easily accessible set-up key located directly on the keyboard. The DECprinter III receive-only version can also be quickly and easily set up by simply raising the top cover panel revealing the Control Function Panel. Set-up parameters can be stored either permanently or temporarily. Set-up allows you to select a variety of features, including:

• Horizontal pitch (lines per inch) and vertical pitch (characters per inch)
• Form length
• Set or clear right, left, top and bottom margins
• Set or clear vertical and horizontal tabs
• Select auto repeat
• Last character view
• Audible features such as bell volume and keyclick
• Baud rate
• Automatic answerback
• Buffer control
• Keyboard and printer character set
• Automatic disconnect
• Local echo
• Auto linefeed
• Modem control
• Secondary channel
• Parity
• XON/XOFF
• Alternate character set
• Break action
• Store/recall

Details on how to select any of the above can be found in the LA120 User Guide or Appendix I of this handbook.

Controls for DECprinter III

The control buttons found on the DECprinter III’s internal Function Control Panel are described below.

Form Len

The LA120 measures form length in lines per form. To determine how long your form is, measure the length of the form in inches, then multiply that by the number of lines per inch (horizontal pitch) you’ve selected. Form length ranges from 1 to 168 lines. For example, if your form length is 11 inches, and you selected a horizontal pitch of eight lines per inch, then the number of lines per form is 88. Each push of the FORM LEN button increments your form length by one line.

Parity

The parity feature enables the printer to test for parity errors in the characters it receives. It also causes the printer to set the parity bits in the characters it sends to the host computer can test the parity of those characters when it receives them.

If the parity feature is enabled and the printer detects a parity error in a character it receives, it will print an error character in place of the character which was changed in transmission.

Sec Channel

The secondary channel feature has two meanings. First, if full-duplex operation has been chosen, the secondary channel is used to indicate the restraint mode. The second meaning applies when half-duplex modem is selected. This secondary feature can be used to indicate the presence of a secondary or reverse channel.

Modem Control

The modem control feature allows the printer to be connected to a modem or acoustic coupler, for use with the dial-up telephone network.

Auto Disc

The auto disconnect causes a modem to automatically hang up the phone when it receives an EOT (End of Transmission) from the host computer, or if the printer becomes inoperable, which is most often due to a paper-out condition. This means a DECwriter III can operate as a printer without the presence of an operator.

XON

This feature enables the printer to generate automatically the XON (DC1) and XOFF (DC3) control characters. The XOFF character asks the host computer to stop transmitting data to the printer. This prevents buffer overflow when the computer sends data faster than the printer can print it. The XON code tells the host computer to resume transmission of data. If the host computer recognizes the XON and XOFF codes, this feature is enabled.

Break

Selecting the break feature causes the printer to send a break signal automatically in response to a paper-out, cover-open, or printhead-jam condition. If your modem system is set up to recognize break, sending a break signal may cause the phone to hang up.

Baud

The DECwriter III and DECprinter III printers offer 14 data rates from 50 to 9600 baud plus eight split baud rates with five different half- and full-duplex modes. This variety of data rates gives you the versatility needed to meet any communications requirements.

Store

Feature settings may be stored in nonvolatile memory and then recalled at any time. It is not necessary for you to set up the operating parameters every time the printer is turned on.

Programming Information

The LA120 uses escape sequences standardized by the American National Standards Institute (ANSI). If an escape sequence is received by the LA120 that is not supported, it is ignored. Using escape sequences, you can control the following LA120 features.

• Printer character set
• Active position
• Horizontal pitch, margins, and tabs
• Vertical pitch, margins, and tabs
• Form length
• Product identification
• Alternate keypad mode

Escape and Control Sequences

The table below describes the function of the most commonly requested escape sequences, and lists the actual escape sequence required. Additional information on escape sequences is in the LA120 User Guide.

There are many other escape sequences you can use. For more information, see Appendix I, the LA120 User Guide, or the LA120 Operator’s Reference Card.

Maintenance

Over the years, DECwriter III and DECprinter III have been reliable in millions of hours of customer use. The printhead provides time-proven reliability. The wires are permanently lubricated for long life and resistance to wear. Wire curvature and support mechanisms are designed by computer simulation for minimal wear and fatigue. The use of constant-current solenoids and a ruby jewel head bearing ensures precise character formation and uniform density of character impression.

To make the LA120 even easier to maintain, all components and subassemblies are easily accessible. If replacement becomes necessary, the power supply and logic electronics are easily accessed by removing two retaining screws in the back panel. Naturally, servicing should be performed by qualified personnel.

Self-test procedure

If it appears that a problem exists in the LA120, you can initiate a self-test. Printing and nonprinting self-tests are available. To initiate a printing self-test procedure:

1. Enter SET-UP mode. The set-up light will flash to indicate that you are in set-up mode.
2. Press the “T” key to initiate the self-test. The LA120 will print out the self-test pattern.
3. To stop the self-test, exist SET-UP or press any character. The self-test will terminate and the set-up indicator will go off.

To initiate a nonprinting self-test procedure:

1. Enter SET-UP mode. The set-up light will flash to indicate that you are in set-up mode.
2. Press and hold “SHIFT” and press the “/” key. The LA120 will perform the nonprinting self-test.
3. To stop the self-test, exit SET-UP or press any character. The self-test will terminate and the set-up indicator will go off.

Operator Troubleshooting Checklist

If your printer is not operating, chances are the problem is minor and you can correct it yourself. Listed below are some of the common problems, their probable cause and the corrective action that you can take. Note: Always turn off the printer before you attempt to correct a problem.

Printer does not start when power is turned on.

• Power cord is not connected, or broken. Check power cord connections; check power cord for damage.
• Power source fault. Check power cord at receptacle.
• Fuse open. Make sure fuse is in place. Replace fuse if blown.

Characters do not print.

• Printer out of paper. Reload paper.
• Printer cover open or ajar. Close cover.
• Printhead too far from paper. Readjust printhead adjustment lever.
• Data set unplugged. Plug it in.
• Incorrect communication set up. Check LA120 User Manual. Make necessary correction.

Light print.

• Printhead too far from paper. Adjust printhead adjustment lever.
• Ribbon out of ink. Turn ribbon over or replace it.

Paper does not advance.

• Paper not loaded properly. Check that the tractor covers are closed and the feed holes are properly aligned.
• Feed holes torn. Reload paper. If paper pulls against the tractor pins or bows in the middle, readjust the right tractor. Sometimes the paper stack feeding into the printer is crooked. Realign the paper stack so that the paper feeds straight into the printer.

Paper tearing on multiple part forms.

• Printhead is too close to the paper. Readjust the printhead adjustment lever for a wider headgap, one notch at a time, and examine the last part’s print impression. Select the setting that gives you the best last part print quality.
• Tractor incorrectly adjusted. If the paper pulls against the tractor pins or bows in the middle, readjust the right tractor.
• Paper not straight in printer. Realign paper.

Printhead jam or printhead does not move.

• Paper or printhead jam. Clear jam and perform reloading paper/form procedure.

Keyboard frozen or printer won’t print.

• Printer cover open or ajar when printer is turned on. Close the cover and turn the printer on. If the condition was caused by a cover-open fault, the printer will reset itself. However, if a paper-out fault condition caused the printer not to print, reset the printer by turning the printer off and then on.

Garbled or double characters.

• Incorrect communication set up. Check that your equipment is compatible with the equipment at the other end of the line.

Additional Documentation

The following documents contain more detailed information about the DECwriter III and DECprinter III printers.

LA120 DECwriter III IPB (EK-LA120-IP)

Illustrated parts breakdown for self-maintenance customers

LA120 Operator’s Reference Card (EK-LA120-RG)

Summarizes set-up features.

LA120 Technical Manual (EK-LA120-TM)

Provides technical details for self-maintenance customers

LA120 User Guide (EK-LA120-UG)

Tells you how to install, use, maintain, troubleshoot, and configure the LA120.

Also of interest are:

PDP-11 and VAX Systems & Options Catalog

Provides you with the most accurate and up-to-date information on currently available PDP-11 and VAX systems, options, and software products. These documents are designed to help you select the right Digital product. European versions are also available.

If you require information not contained in these documents, contact your local Digital representative, dealer, or distributor.

Specifications

Performance Characteristics

Paper

Communications

Power Requirements

Operating Environment

Physical Characteristics