HP-71 Diagnostics

[Dave Frederickson]

One feature of the Diag ROM and Port 1 is that they be capable of disabling the system ROM. They do this by shorting the Output Disable signal, OD, to VDD.

This is all discussed in detail in the FRAM71 Manual Chapter 11, Using the SYSRAM feature.

The Diag ROM module has the OD pin shorted to VDD and when plugged into Port 1 it disables the system ROM and allows the Diag ROM to take-over.

If you have any further questions regarding the Diag ROM I suggest you contact the seller as he was on the development team for the 71B and probably knows a thing or two more than we do.

Dave