QProbe - a QBUS signal adapter

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

So after UniProbe, I also designed a "QProbe".

qprobe total head

The card has these features:

  • it acts optionally as bus terminator via changeable resistor packs.
  • it visualizes the QBUS signals. 
  • Two display modes:
    a) ADDR and DATA are demultiplexed, INTR and DMA 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 with 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.

Read on!


Title Author
QProbe - Introduction Written by Administrator
QProbe - QBUS Interface Written by Administrator
QProbe - Blinkenlight Header Written by Administrator
QProbe - Logic Analyzer Interface Written by Administrator
QProbe - Programmable Logic Written by Administrator
QProbe - Getting One, Building, Downloads Written by Administrator
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