[SiriusHardware]

I've also made a bit of progress with the 2716 / 28C16 to PET PROM socket adaptor. I've gone for the 'stacked sockets' approach.

On the PET PROM sockets, pin 21 is CS3 and tied to +5V. On the 2716 and 28C16, pin 21 is VPP and WE respectively, both of these pins need to be held at +5V for their respective devices to work in read mode, so no alteration is required there.

PET PROM socket pin 20 is the active-low CS1 and the same pin on the 2716 and 28C16 performs an equivalent active-low chip enable / output enable function.

The only aberration is pin 18, which on the PET PROM socket is A11. On conventionally pinned devices this pin is another active-low chip enable / output enable, so in this case the pin joining the upper socket pin 18 to the lower socket pin 18 has been snipped and taken by a small wire link to pin 20 of the upper socket so that the active-low enable signal going to pin 20 also goes to pin 18 on the substitute device.

Since the 2716 and 28C16 are 2K devices, this means they don't have an A11 pin so if plugged into the UD9 socket for example any code programmed into them will appear at both F000- and F800- I don't see this being a problem. The test code I have is intended to run at x800 onwards, in the upper half of the block.