I bought some terminals, AT&T Model 56C 610 AAA, which when turned on say:

BASE CARD:
              PROCESSOR : PASS
              EPROM     : PASS
              256KRAM   : PASS
              SSI       : PASS
              VCP       : PASS

then the screen clears and the message

                        WAIT

appears on the bottom line.  Ad infinitum.

They have locks on the right side of the display, and they just sit
there in the WAIT mode, no matter which position the key is in.

They have (only) an RJ45 (8 pin) jack for connection to the outside
world, (in addition to the keyboard jack).

Can some helpful soul tell me WHY they have 256K of RAM, and what
"SSI" and "VCP" mean?  Anything else?

These terminals are (DEPENDING ON THE LOGO) 6539 MFT (Multi-function)
         terminals.  They are, unfortunately, designed to work with the 6500
         series of multi-function cluster controllers (MCC).  The "SSI" you
         observered in the self test stands for "standard serial interface"
         and is a 56kbps serial link implemented in proprietary silicon.

         The MCC was AT&T's (and later MEMOREX's) version of the 3270 IBM
         clusters, such as 3274 and 3174.  Each MFT could support sessions
         with up to 16 hosts (4 at a time in separate windows) ( I am typing
         this reply on one in an asynchronous window emulating a VT220
         color terminal. )


	[Archiver's Note:  perhaps he means a VT241, because a real DEC VT220
	 has only a monochrome screen, either green or amber. ...RSS]


         Without the cluster controller the terminal is non-functional.
         All the terminal fuctionality was downloaded from the cluster
         and the WAIT prompt would change to LOAD when the unit is
         connected to a functioning cluster controller.  The only program
         in the stand-alone terminal are the ssi drivers, and self-test
         programs.  For example if you depress any keyboard key when
         powering up, the keyboard and display test mode will be entered.

         Note that each key depressed gives a code and the release also
         gives a code, different by one bit.  The repeat function was
         implemented in software so that any key could repeat, depending
         on the application.

         This is probably more information than you needed on devices
         that are useless without the controller but are actually robust
         and reliable when hooked to a controller.  Features included:
         synchronous (bysync,TOKEN RING, and SNA), async up to 19.2,
         programmable windows (SIZE, POSITION, COLOR) user programable
         PLAY keys (used to record and replay long key sequences)
         printer support with user route selection, transfer of data
         between windows (including ASCII to EDCDIC conversion),
         incoming asynchronouys support including host switching
         and protocol conversion, and many others.

         The 6500 product line was introduced and manuctured at AT&T's
         Little Rock Operations Center until the product line was purchased
         by Memorex-Telex several years ago.  Memorex-Telex still supports
         the product and has continued developing new hardware and features.