April, Merlin Gerin - French 70s/80s PLC

Hardware
1

I found another interesting very early PLC series. APRIL, made in Castres by Télémecanique up to 1993. Now owned by Schneider. The earliest card I found for sale is from 1979 and the cards had a light green front. Here the typical SMC 600 rack
april
(short clip on Matthew D. Smith on LinkedIn: 😆 OT datacom archeology time! 🦈 Look what we found on the other side of…)

The smalles ones (also rack) are SMC 25, 35. Other series were 2000/3000, 5000/7000 (68k). I think all cards were labelled with SMC81 - Castres.
Earlier models at least since 1975 were PB15 (8031 CPU), PB 80, PB400… by Merlin Gerin/April. DOS software was called GRAL. I found small programming handhelds made by Oyster Terminals (UK).

I searched for manuals, very difficult with “April” and found some on this forum (I found some other rare stuff there before) in French.
https://www.plctalk.net/threads/april-pb400-plc-merlingerin.123969/

merlinpb400code
merlinpb400code633×878 46.7 KB

Luckily, I know French but I’m not used reading French PLC terms. SI/OU is probably AND and OR. OU\ is NOR. Some more (internal) instructions.

I also found a Mitsubishi programming console for the PLC MELSEC F1. Melsec is after AEG, Siemens and Klöckner Moeller the forth of the most used PLCs (then, late 80s) in Germany. I haven’t found that console before. At least adresses in octal on F-12R, F-20M.
The console can be plugged onto the PLC and showing the instructions stored. DOS Software MEDOC. Manuals officially on mitsubishi. Clip in English

melsec
melsec745×647 283 KB

2

I took a closer look to the programming of the French PLC APRIL. I first assumed that SI must be AND and I wondered what ET is, as ET is French for AND.

SI 050
SI/ 051
ET 060

Ladder logic
50 51 60
-] [-]/[–()

That is what’s happening, the operation is after the operands, so I think reverse Polish notation

(IF input 50=1
IF i51 is NOT 1
AND)
THEN LOAD OUTPUT 60=1

Almost all other PLCs I’ve checked starting a rung with either AND (one starting with OR), Klöckner-Moeller and Mitsubishi starting with a LOAD instruction but then AND as well.
A typical Siemens (S5) instruction list would look like this
:A I 0.1 //AND input - in German: U
:AN I 0.2 //AND NOT - German: UN
:= O 0.0 // = output

Function block diagrams and logic gates have lines left or on top of the boxes, so having the function last like the French one would represent that order.
There is already programming in GRAFCET, what I thought would be much later. There are definitions at the beginning, SAUT are JMP either relative or direct. I haven’t searched for software/compiler yet. But often it’s not that useful without hardware. So the manuals are much more of interest.