According to a 2010 comment on a thread at the Sekine Bicycle Database, the
DS80 indicates that the frame is from the Dodsun Bicycle and Machinery Manufacturing of Taiwan.
A comment on a thread at OzBMX says:
DS is Dodsun who made frames for many brands including Redline, Cycle Pro and Crossrider
A Google image search for Dodson touring bicycles shows the usual assortment of random frames.
Finally, a post on Bike Forums is most informative:
Based on the location of the serial number [bottom of seat tube], this will probably be a Dod Sun of Taiwan serial number.
The first line of the serial number will 4 characters, widly spaced. The first two characters will be "D" and "S" for Dod Sun. The next character will be a number for the year of manufacture of the frame, probably "9", "0", or "1". The last character will be a number "0" or "1", the tens column of the number for the month that the frame was made.
The ones column for the month is the first character of the second line. The rest of the characters are numbers.
Based on this information, which may or may not be accurate, your frame could be a Miyata built by Dodsun in Taiwan in June of 1988. Or, it could be something completely different.