The INTERSPEC is a BUS Expansion module, developed and produced by DCP Microdevelopments in 1983*

I bought mine in 1984, primarily to control display Meccano and other models.

Having recently cleared the loft, I found and restored my Spectrum and then rediscovered the INTERSPEC. Sadly I could not fine the original instruction manual and there did not appear to be any available on the Internet. I found a reference to one at the South West Retro-Computing Archive: I contacted them and they kindly sent me scanned copy. I OCR'd the document into WORD. Some editing, corrections and re-drawing of the graphics resulted in my version which you can download a PDF version of here:

In this video, I demonstrate the Inputs and Outputs of the Interspec with the hardware and software examples shown in the manual. I could not test the DCP Bus as I have no other DCP units to connect it to but will experiment with the guidance shown in the manual.