Commodore 75BM13 monitor ?

I recently acquired a Commodore 75BM13 monitor. Its' signal-in port is a female 6-pin Din like the C64 serial port. It was manufactured in 1986. The 1902 (non-A) also had a 6-pin port and a cable with an 8-pin on the computer end but I tend to doubt this was a low-cost alternative. The M13 part of the model # undoubtably stands for monochrome 13". I've been unable to find any info on it other than a few oblique references in the CBM newsgroup and a Commodore monitor list with no specs and a question mark opposite a similar model 76BM13. Anyone know what this model might have been used with ? When looking thru my cable stash I came across a cable with the same pin-out on both ends and also "monitor" printed on one end and "computer" on the other end. It didn't come with the monitor and I'm curious what it may be for. Anyone recognize it ? Thank you. I'm no longer on the list but browse it occasionally when I have time. Lawrence