When repairing DEC PDP-11s there's always the need to see whats happening on the main system bus. On newer PDP-11s and Micro-VAXes this is the QBUS.

So after UniProbe, I also designed a "QProbe". And see below for "QProbe2023"


qprobe total foot

qprobe total head


The card has these features:

  • it acts optionally as bus terminator via changeable resistor packs.
  • it visualizes the QBUS signals. It has selectable display modes:
    a) ADDR and DATA are demultiplexed, INTR and DMA signal pulses are elongated to be visible.
    b) "passthrough": LEDs just show state of bus lines.
  • Pin headers provide access to signals via logic analyzer (LA) or multimeter.
  • Patch field to connect LA probes to QBUS signals in a clean way. LA ports have changeable impedance-matching resistor packs.
  • LED drivers and demultiplexer logic realized with two EPM240T100 CPLDs. These can be programmed with own logic via an onboard JTAG header and Intel QUARTUS tool.

 See QProbe here in action: connecting a 11/23+ and my ZEROPLUS logic analyzer:

qprobe in use