ThePDP-14 was a specialized computer fromDigital Equipment Corporation’s Industrial Products Group designed to replace industrial level relay controls for machinery and machine tools that performed repetitive tasks. It was specifically designed to function in the harsh electrical environment encountered in facilities where electric motors,solenoids andarc welders were present, a significant adversity for normal computer electronics. The PDP-14 was specifically designed to be the first level of factory automation, functioning as aprogrammable logic controller (PLC), through its ability to communicate with a standard DEC PDP-8minicomputer.[1][2]
The first unit was delivered in June 1969 and used to control agear grinding machine.[3] Its design as a "programmable machine controller" was patented in 1973.[4]
The PDP-14 was designed to processBoolean equations, usually expressed as “ladder diagrams” and as such had a programmable read-only program (PROM) memory. Programs were developed using a PDP-8 then tested using a direct connection to the PDP-14. The PDP-14 was put into a check out mode where instructions were provided by the PDP-8. Following checkout, the PDP-8 provided the instructions to be put into the PROM.
Later versions (for example, the PDP-14/30, whoseinstruction set was notbinary compatible)[5] are based onPDP-8 physical packaging technology. There also was a PDP-14/35[6] and a lower cost/reduced I/O capability PDP-14/L.
The12-bit PDP-14 could hold a maximum of 4Kwords for instructions. The system's configuration included a control unit and a number of external boxes:[5]
Hence the combined usable output address space of theO-boxes,A-boxes andS-boxes was 255 or fewer.
The PDP-14 has seven 12-bitregisters:[5]
IRPC1 &PC2MBSPAREINPUT andOUTPUT.Among the PDP-14 instructions were:[5]
TRR – to move data between some (but not all) of the registers – TRansfer Register (contents).PC1 andSPARE have increment and decrement capabilities, permittingTRR to modify the value loaded into the register.JMS – JuMp to Subroutine – at the address specified in the following 12-bit word,saving the return address inPC2JMR – JuMp to RETURN from a subroutine, jumps to location saved inPC2.[5] In effect, JMR is aTRR in whichPC2 is transferred toPC1.SKP – SKiP – is aTRR in whichPC1 is incremented by 1.There were alsoTEST instructions (Test if something is ON or OFF) andSET instructions (SYN – Set "Y" oN, SYF – Set "Y" ofF).
The original PDP-14 required that programming be done by DEC.[7]
Subsequently,[7] software development for the PDP-14 was done on another system, thePDP-8. A PDP-8 program named SIM-14 allowed for simulating the PDP-14.
