EDUC-8ME Update

[Steven Pietrobon]

I've made a fairly large update to EDUC-8ME, a memory and I/O port expansion for EDUC-8. I have moved the unit selection and address decoding logic from E8ME/D to E8ME/I. This means that E8ME/D is only required in the first EDUC-8ME unit, reducing complexity if more than one unit is used and reducing the load on the switch register. I've also updated the E8ME/M boards to allow the option of using 2102 or 2125 1Kx1, 2147 4Kx1 or 2167 16Kx1 SRAMs. There are also many other minor updates. You can download the updated paper and schematics from the link below.

http://www.sworld.com.au/steven/educ-8/educ-8me.pdf

Next up is documenting the schematics for EDUC-8L, which adds a link bit to EDUC-8.

[Steven Pietrobon]

I've made another update to EDUC-8ME. I found there was a bug in the design due to the use of the OPR+IOT signal in E8ME/B. This signal can be high during EXAMINE and DEPOSIT and will thus cause an incorrect field to be addressed since the 2-bit MEA address could be non-zero. This has been corrected, along with many other minor improvements. I've also managed to delete one chip in E8ME/D! You can download the updated PDF from the link below.

http://www.sworld.com.au/steven/educ-8/educ-8me.pdf

I've also updated the design of EDUC-8L which adds the link bit and its associated instructions. I've also added other instructions that were used on the PDP-8 as well as one new instruction that wasn't included! Here's the list of the 16 new instructions.

715 DAC (decrement accumulator)
712 OSR (OR switch register with accumulator)
706 BSW (byte swap, exchange AC[7:4] with AC[3:0])
703 RLL (rotate link left through AC register)
713 CLL (clear link)
707 CML (complement link)
717 STL (set link)
731 RTL (rotate link twice left through AC register)
725 RTR (rotate link twice right through AC register)
732 SNA (skip on nonzero accumulator)
726 SPA (skip on positive accumulator)
736 SNA.SPA (skip on non-zero and positive accumulator)
723 RLR (rotate link right through AC register)
733 SZL (skip on zero link)
727 SNL (skip on nonzero link)
737 SKP (skip)

I'm still working on the documentation for EDUC-8L and will send that to the group once it is finished. Once that is done, I will be doing another update of EDUC-8ME that will include the option of adding interrupts! All these updates will make EDUC-8 into a quite powerful little machine.