HD3P01M1 with piggback eprom

[johnh]

Whilst poking around the recycle skip at work.

I found some old low speed modem shelf from the mid 80's. 

Out of dozen cards, 3 had these plugged into them. The rest had had mask programmed CPU.
No special label on the card.

Why would you use these, which would cost more than the mask programmed cpu's?

[NiHaoMike]

Most likely some early production units or a new firmware revision.