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Hi,
A while back I obtained this great condition mill, and spent a good while getting the original B control and parajust vfd to function. I guess I've had a good few years of use, and learned all that old school stand at the control panel block entry programming system. Thank goodness for CAD systems making it simple to workout profile tangent points and arc centres. What I have learned is the the machine is good, but  for programming prototype parts a bit of a liability, especially if you make changes in the middle of 100 block programme. Not smashed anything, but embarrassed myself.

Always did have a plan to retrofit the control, but now is the time to do it. I know that these old machines have been covered a few times in the forum, but the questions I am bumping into don't seem to be quite covered hence the reason for a new Topic.


My plan is to insert a chassis containing some Mesa boards, and a Raspi 5 in and to make an intermediary interconnection board that accepts all the Hurco edge connectors that go to the B control. From the picture you'll  I've done most of the preparation already. 
The Mesa boards are 7i92T, 7i77D and 7i73  

The sub board accepts the original connectors, and breaks out into solder pads where I can add appropriate wires to connect into the Mesa items. 
My maybe silly idea on this, is that if I don't cut any wires, I can always revert to the historical system, to prove to anyone's  passing grand kids that there is life still in 1980's computing.

I'd like also to use the pots and original pulse generator retained in place in the pendant panel, as well as as the still working fvd and servos etc, in fact everything that's operational and can work with linuxcnc. ( I accept that the encoders will need many more lines and have 2000 cpr ones in stock.)

Question 1 Limit switches
The existing ones are 5volt solid state devices, and the output floats at 5volts, pulled up by a 470ohm resistor in the Hurco control, until triggered where it falls to zero and switches on an LED in an optical isolator which signals the servo to stop as well as telling the operating system that the axis travel has been exceeded.

My initial idea was to connect this output into the 7i77, but I now believe that the field IO terminals TB7/8 won't trigger at only 5 volts, so I propose to use the 7i73 P2 connector, pins IN8 thru' IN15 which are 5 volt tolerant, but with 4.7 kohm pull up resistors.

I'm not the greatest at electrics, so would appreciate your advice.

Thanks

Look mate when the guys were trying to help you with your homing issue you refused to supply your ini & hal files. Do you get it ?

Just for the record, I never did get the tape to consistently run. Bought a tape emulator from Buddy Maughon at Accurate Machine Tool Serv. Initial issue was some of the 5volt regulators were marginal, so I replaced them all with PSU5 LM323 replacements from ezsbc.shop/.
I had also to replace a number of chips on several of the boards, eg watchdog timer, x axis counter, y axis encoder as the scale had a chip out of it and counted incorrectly, relay optical isolators, then all the tantalum caps on the 2 parajust control boards to get the spindle to run, but in the end, it works accurately as an original Machine and still does. But now started to Linuxcnc it in a sympathetic way.