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".
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.