LSI-11/2 microcode source

Heinz wrote: Reading the MICROMs wouldn't be that difficult. But it's not the whole story. The control chip has two metal-mask PLAs ("translation arrays") that can cause PC changes even when the current microinstruction is not a branch, based on two 8-bit translation registers and various other inputs. I can envision two ways to dump the translation arrays. 1: Capture a whole lot of logic analyzer traces covering both the Qbus and the microinstruction bus while executing a variety of PDP-11 software. Write software to parse the traces, identify translation branches, track the expected translation register contents, and build up logic equations. This is a lot of work and wouldn't be guarateed to come up with identical PLA equations, though if you run enough traces through you'd probably get close. 2: Deencapsulate a control chip with fuming nitric acid, take a high resolution photomicrograph, and spend a lot of time studying it to figure out the topology of the PLAs. You can't, because the translation arrays are different in the LSI-11, Pascal Microengine, and WD-16. The data path chip of the Pascal Microengine and WD-16 are the same, but I'm not 100% certain that it's the same as that of the LSI-11. Also, the system-level interface of the LSI-11 and Pascal Microengine are different. There are four bus control signals from the MICROMs that get decoded for bus control, and they are not used identically in the LSI-11, Pascal Microengine, and WD-16. Even if you swap the control chip along with the MICROMs, the Pascal Microengine doesn't know how to talk to a Qbus. Eric