Absolutely. There has been a recent trend to run tests on the hardware used in the BBC micro to learn details that are not specified in the manufacturer's data sheet and then make emulations implement those details, at least in part because experience has shown that software is sometimes written to rely on these details.I think the point that some others were speculating about is that unless the 1770/2 chip is reset either via the MR (master reset) input or via accessing the relevant registers, the chip will be in an undefined state with regards to the output pins that feed the NMI signal to the rest of the machine.
That does not mean, when an IC behaves differently from another one of the same type in a way that is not specified in the data sheet, that it necessarily has a fault or some kind of bug. People explore the undocumented behaviour of an IC and then rely on it, in either hardware or software designs, at their risk.
In the case of the Watford DDFS that is intolerant of some variants of the 1770, the bug is in the Watford design. It needs to reset the NMI line either in hardware, via the MR line, or in software via the registers.
Statistics: Posted by Coeus — Wed Apr 23, 2025 12:56 pm