1. Hardware
    Registers  Instructions 

2. Software

3. Photos

4. See also

5. References

6. External links

The PDP-14 was a specialized computer from Digital Equipment Corporation. Unlike DEC's general-purpose computers, which are simply called computers, this unit had no data memory or data registers and was intended as an industrial controller - a Programmable logic controller (PLC).

Its instructions can test Boolean input signals, set or clear Boolean output signals, jump conditional or unconditionally, or call a subroutine.

I/O is line voltage.

Later versions (for example, the PDP-14/30, whose instruction set was not binary compatible)^[1] are based on PDP-8 physical packaging technology. There also was a PDP-14/35^[2] and a lower cost/reduced I/O capability PDP-14/L.

Hardware

The 12-bit PDP-14 could hold a maximum of 4K words for instructions. The system's configuration included a control unit and a number of external boxes:^[3]

• I-boxes (BX14) were for discrete inputs from the controlled system. Up to 256 input sources could be addressed.

• O-boxes (BY14) could control up to 255 actuators in the controlled system.
• A-boxes could be filled with timer modules for controlling time-driven events or retentive storage modules which were not cleared with power loss. A-boxes occupied the output address space along with the O-boxes.
• S-boxes were essentially the same as the O-boxes, but there was no real output device. This enabled storing intermediate results. S-boxes also used the shared output address space.

Hence the combined usable output address space of the O-boxes, A-boxes and S-boxes was 255 or fewer.

Registers

The PDP-14 has seven 12-bit registers:

• IR
• PC1 & PC2
• MB
• SPARE
• INPUT and OUTPUT.

Instructions

Among the PDP-14 instruction were:^[1]

• TRR - to move data between some (but not all) of the registers - TRansfer Register (contents).

PC1 and SPARE have increment and decrement capabilities, permitting TRR to modify the value loaded into the register.

• JMS - JuMp to Subroutine - at the address specified in the following 12-bit word.
• JMR - JuMp to RETURN from a subroutine, to ADDRESS+1 of the most recent JMS.

effectively, in modern terminology, JMS pushed the current instruction address onto a "stack"^[4]

and JMR popped the return address.^[1].

In effect, JMR is actually a specific TRR in which PC2 is transferred to PC1.

• SKP - SKiP - is a TRR in which PC1 is incremented by 1.

There were also TEST instructions (Test if something is ON or OFF) and SET instructions (SYN - Set "Y" oN, SYF - Set "Y" ofF).

Software

The original PDP-14 required that programming be done by DEC.^[5]

Subsequently,^[5] software development for the PDP-14 was done on another system, the PDP-8. A PDP-8

program named SIM-14 allowed for simulating the PDP-14.

Photos

• PDP-14
• PDP-14's M740 Instruction decoder module
• PDP-14's M745 PDP-8 Interface

See also

• PDP-16

References

External links

• PDP-14 User's Manual
• includes information about interfacing options

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