The Tektronix 50M30 is a 16-bit I/O card for the MI5010.
From Tekscope Volume 13 Number 3, September 1981 page 6:
The 50M30 Programmable Digital 1/0 Card features 16 channels each of digital input and digital output. Both input and output are TTL compatible. Typical applications for this card include interfacing with relay drivers, switches or custom keyboards, BCD data from non-IEEE-488 instruments, and static binary words.