MICROFORUM

Hi to all,
I have created detailed schematic diagram of backplane at HP9845B. The backplane has part number 09845-66502. It has four slots for external interfaces. On the board are TTL buffers for inputs- / outputs data. I would like know a communication between the data buffers and CPU.

I would like know more about p-variable at HP9825. My questions:

• are the p-variables just an option or are they available by default?

• are the p-variables in 9825 model A or model B or both?

• what is the benefit of using p-variables and r-variables?