How the Entrex 480 / Nixdorf 620 Boots

March 24, 2024 From Bruce Ray with Wild Hare Computer Systems / NovasAreForever.org:

The standard DG/DCC Data Channel device [DCH] tape/disk bootstrap program consists of only 3 instructions:

375/ 062677   IORST

376/ 0601<xx> NIOS <device code>

377/ 000377   JMP 

This is the program initiated by the PL switch on the 'standard' machines

DCH device controllers are designed to boot from record/sector zero of a tape/disk drive into location 0 onward, and therefore overwrites the JMP . instruction at location 377.  Any standard bootable DG/DCC tape/disk [and I would assume Entrex] successfully uses this model.  If a faithful image of a tape/disk is created and appropriately configured in an emulator, the system should be 'bootable'.  A correct SimH-compatible tape restoration works on all of the very-diverse systems I work with, and likewise for disk images and appropriate disk emulation configuration.

Therefore, if a known "bootable" tape is accurately recovered to SimH-compatible format, the resulting contents should behave exactly like the original hardware if the various parameters are met.    This is the basic approach successfully used over the decades for handling even the 'weirdest' client situation.

Once the controller is started [i.e. NIOS <device>] the controller will transfer words from the device to main memory automatically.  Even if an extreme custom hardware modification were made to the front console's program load logic, the examination of the tape/disk record/sector zero might reveal more information, faster, than trying to grok custom hardware modifications.  Knowing the exact [human] operator procedure to bootstrap the system would reinforce

the decision to attack the problem either bottom-down or bottom-up.  Top-down In this case would be to start with a known good accurate copy of the tape/disk media in question, bottom-up would be dissecting schematics to discern the forest from the trees... 

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We provided Bruce with these two recovered SimH-format 9-track tape files:

Entrex_Nixdorf_620_Save_PRIX_22-01-87.tap

Entrex_Nixdorf_620_Master_Didos_1_genere_08-10-83.tap

to which Bruce replied with these glorious preliminary results:

Pertec 9-track Formatter "Key To Tape" device

This device is NOT part of the Entrex 480 system, 

but in order to understand a "Key-To-Disk" system like the Entrex 480, 

here is a "Key-To-Tape" stand-alone device to illustrate the differences.  

Notice the "029" keyboard layout?

Acquired from Orrill's Auctions, Los Angeles on March 12, 2024

IBM 029 Keypunch Keyboard vs Entrex Data/Scope

Compare this keyboard to the "029" keyboard option for the Entrex Data/Scopes (Keystations).  As the Entrex 480 advertisements state, this keyboard layout was a featured option on the Entrex Keystations so that operators who were used to the IBM 029 keypunch keyboard layout were able to transition to using the Entrex Data/Scope without any re-training on the keyboard layout.  How cool was that?!