RXV21 questions

[Douglas Taylor]

I have 2 RXV21 RX02 controller boards.  They were bought to be used with 
the RX02 emulator, the one on github by AK6DN.

Finally, I finished one of the emulator boards and tried it out on a 
PDP-11/03 and found that one of the RXV21  boards worked and the other 
didn't.  I assumed the one board was bad.

Yesterday I tried the RX02 emulator in a BA23 with a 11/53 cpu (I also 
tried a 11/23+) cpu.  What I found is that the one that worked in the 
11/03 didn't work, while the other board kinda worked.  I could do a 
DIRECTORY and DUMP from RT11, but I couldn't boot the RX02 in the 
microPDP-11.

Today I ran into Chuck Dickman's web site that talked about the Etch 
versions of the board and which would work in a microPDP-11. He showed 
how to convert an Etch 'D' board to work in a microPDP-11.

I have Etch 'C' - this is the one that works in the 11/03, and an Etch 
'D'.  My 'D' board isn't exactly like the 'D' board he shows.

What are the changes to the 'D' board that he outlines?  What is exactly 
the reason why the 'C' works in the 11/03 and why an 'F' or modified 'D' 
is needed for the microPDP-11?

Doug