QBUS Notes

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This page captures my rough working notes regarding QBUS systems.

You probably won’t find anything greatly useful here. It is mainly a place for me to records things that I seem to continually forget the details of!

BA11-NC Chassis

This is a 9 row 18-bit ABCD chassis. So dual-height cards get aligned with the left-hand edge of the backplane (the AB slots), and there is no need to put grant continuity boards (M9047) in the unusued CD slots.

The Processor board goes in the top slot.

Sigma Information Systems BA11 Chassis

I like this chassis because it has PWR, LTC, BOOT and Halt switches on the front panel, as well as providing access to the QBUS boards through the front panel.

This is a 9-row [XX]-bit ABAB chassis. The processor board goes in the top left slot. The grant continuity chain goes in serpentine fashion (Row 1 left, Row 1 right, Row 2 right, Row 2 left, etc).

Hooking up a minimal PDP-11/23 system

A minimal 11/23 system that boots RT-11 V05.03 from an emulated TU58 drive can be put together using the following:

  • M8186 (11/23 Processor) in the first AB position
  • M8044 (64KB / 32KW RAM) in the second AB position
  • M8043 (4-Port SLU) in the third AB position
  • M8012 (BDV11, modified to hold 11/23 interactive boot ROMs) in the final row
  • Serial Terminal connected to left-hand port of M8043 at 9600,N,8,1
  • TU58 emulator (running on an MSDOS PC) connected to right-hand port of M8043 at 38400,N,8,1

I’ve found that this system will successfully boot RT-11 regardless of:

  • Empty slots (without grant cards) before the BDV11, which is positioned in the final slot
  • Whether the LTC is enabled or disabled on the M8186
  • Whether the LTC switch is on or off on the Sigma Information Systems chassis
  • Whether the left-hand switch on the BDV11 is in the left or right position

If the RT-11 boot fails part way through (before there is any sign of life at the console) at Block 164, two things that will definitely cause this are:

  • No grant continuity between the M8043 and the other two cards (M8186 and M8044)
  • SLU card with the vector set to anything other than 300