LINCtape/DECtape Conversion Program

This document describes the PRTC12-F program, designed for the Digital Equipment Corporation (DEC) PDP-12 computer equipped with the TC12-F tape option. Its primary function is to enable the user to read and write DECtapes in the forward direction, even if these tapes were originally formatted on PDP-8, PDP-9, PDP-10, or PDP-15 computers.

The program addresses several key differences between the PDP-12's LINC format tape and other DECtape formats, including reversed tape direction, reversed tape head polarity, reversed channels one and three, and a different 12-bit data transfer configuration. While the TC12-F hardware decodes "block mark" (BM), other functions like data flags, bit shuffling, and checksum computation/verification are handled by software.

Written in LAP6-DIAL language, PRTC12-F occupies memory locations 3500 through 7712 and is non-destructive, restarting automatically or manually at address 4020. To operate, users start the DIAL system, load the program (specifying a tape unit 0-7), and then interact with a series of on-screen prompts. These prompts cover program introduction, and "READ" and "WRITE" questionnaires for defining the operation (e.g., number of blocks, tape format, unit number, starting block, and whether to check parity).

The program supports nine distinct data transfer modes (MODOPs), allowing various combinations of data transfer between PDP-8, PDP-12, and PDP-9/10/15 (referred to as 'N') systems, accommodating different word/block sizes and block packing arrangements. The document details the specific read and write procedures, including control word skipping, data assembly, parity computation, and checksum verification (for reads).

Key restrictions of PRTC12-F include:

1. Data can only be read and written in the "forward" direction.
2. Data is not checked after being written to tape, with the exception of LINCtape transfers.
3. A maximum of 2000 (octal) blocks can be transferred in a single operation.