Type 646 Line Printer

This document describes the Digital Equipment Corporation (DEC) Type 646 Line Printer Control, a program-controlled buffer interface designed to connect the PDP-6 digital computing system with the 646 Line Printer (a Series 5 ANelex printer). The manual provides comprehensive information on the control's theory of operation, installation, operation, and maintenance.

The Type 646 Line Printer Control accepts five 7-bit ASCII-coded characters at a time from the PDP-6 via the I/O bus. It decodes these characters, sending printable data or formatting commands to the printer. Control characters enable various functions such as horizontal tabbing (with preselected increments), carriage returns, form feeds, line feeds, and multiple vertical tab line advances. Illegal characters are detected and ignored. The control also communicates its operational status (e.g., ready, busy, printer errors, buffer overflow) back to the PDP-6 through a priority interrupt system.

The control unit is physically housed in a standard computer cabinet containing 45 DEC system modules and operates on -15 VDC and +10 VDC. The 646 Line Printer itself is a 1350-pound unit capable of printing 120 columns at up to 300 lines per minute, requiring independent 115 VAC power. The manual details the signal interfaces for both the PDP-6 I/O bus and the line printer, including device selection codes, command pulses, and status signals. Maintenance sections outline preventive procedures (mechanical checks, power supply tests) and corrective troubleshooting steps (diagnostic programs, signal tracing, repairs, and validation tests) using standard tools like multimeters and oscilloscopes.