This is slightly inaccurate:
https://wiki.mobileread.com/wiki/Data_Discman
All models can play mini (8cm = 3.15") Audio CDs, but the later ones can play "audio files".
I have now the first Western version, the DD-EX released in 1991. The DD-1 was in Japan in 1990.
It takes 9V DC at about 0.5A. The battery pack is missing, which is either 6x AA cells or rechargeable (likely NiCd).
There is video out (4:3 mono in 625 lines 25fps interlace or 525 lines 30 fps interlace). The LCD panel (256 x 256 pixels = 30 characters x 10 rows) is blank. Blacklight works.
The included title works.
The caddy opens easily and is like a double thickness 3.5" floppy. There is an official Sony DOS emulator (try Archive Org) and the discs removed from caddy work in any regular drive that takes 8cm discs as well as regular size.
There is a demo version of an authoring tool (size limited) and then you burn a CDR. It takes text files and images (which are reduced to 256 x 200 and 1 bit).
They later expanded the features of the system and the screen. Initially plain text of 30 characters by 9 lines and a 10th menu line for F1 to F5 keys with 1 bit images.
So far I've found
DD-1EX (256 x 200 or 256)
DD-10EX
DD-10BZ
DD-8
DD-20
DD-25
DD-35 (Last model sold up till 2000)
Japanese
DD-1
DD-MR10
DD-S35
DD-75SP
DD-95
DD-300
DD-350
DD-S1000 (Color 320x240)
See
https://retrostuff.org/2019/05/22/so...iscman-repair/
User and Service for the DD-1EX