I found some info:
https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1091816The DE/280A accepts ASCII signals for
the normal upper and lower case 96-
character set and also for the expanded
set, which, includes Katakana and
selected ECMA characters. An on-board
microprocessor handles decoding,
character generation, display buffering,
cu,rsor control, auto flashing of any or
all characters, refresh, programmable
reset, self-test, and a blinking visible or
invisible cursor. All drive electronics
are included along with necessary
power conversion circuitry to adapt
incoming +5 Vdc to tube voltages.
Jumper selectable Bd rates (1200,2400,
and 4800) are available for serial interfacing. Parallel interface is also standard. RS-232 voltage levels are optional. All character positions are
randomly addressable. One additional
feature of the DE/280A is that it is the
same form, fit, and function as DECO's
single-line 40-character module, the
DE/245A. Consequently, either display
can be used in a design without any
changes in dimensions or user software.