From: Ben Cranston <zben%umd5.UUCP@seismo.CSS.GOV>
Newsgroups: net.wanted
Subject: Re: Manual for ADM-3 Terminal (long ~130 lines)
Date: 26 Nov 85 17:44:22 GMT

ADM3 "Internal" switches (at back of main board)

SPACE-ADV
In SPACE position, selects destructive cursor.  Pressing the space bar
or receiving a space code ALWAYS overwrites the display memory location
with a space code and advances the cursor.

In ADV position, selects non-destructive cursor between a Return and 
subsequent Line Feed only; the cursor may be advanced but a space code
does not overwrite display memory locations.  The space code is 
destructive between a Line Feed and the next Return.

UC DISP-U/L DISP
In UC DISP position, allows display of upper case characters only.  Lower
case codes are transmitted as such but are converted to upper case for
display.  If lower case is not installed or if it is not to be utilized,
the switch must stay in the UC DISP position.

In U/L DISP position, allows display of upper and lower case characters if
the terminal is equipped with the Upper/Lower Case option.

[This option is a second plug-in char gen ROM and an additional 2102  
 memory chip -zben]

DISABLE-KB LOCK
In DISABLE position, prevents locking of keyboard.

In KB LOCK position, allows keyboard to be electrically disabled (locked)
by remote control codes.

[SI locks, SO unlocks -zben]

DISABLE-CLEAR SCREEN
In DISABLE position, prevents clearing of the displayed information except by
executing repetitive line feeds.

In CLEAR SCREEN position, allows computer to clear ADM-3A screen by 
transmitting a control code (CTRL Z).

50Hz-60Hz
Selects 50Hz or 60Hz display refresh rate; must be set to correspond with
input power frequency.

12 LINE - 24 LINE
If terminal is equipped with 24-line display option, this switch may be used
to select 12 or 24 line display.

On terminals with standard 12 line display this switch must be set to the
12 line position.

[This option is 7 or 8 additional 2102 memory chips.  The 7 or 8 depends on
 if the upper/lower case option is also installed. -zben]

CURSOR CONTROL
In the ON position, this switch selects a moveable reverse block cursor
which accesses any area on the screen.

In the OFF position, this switch selects the standard double-underline
cursor.  In this mode, data is entered from the bottom of the screen.

Upward scrolling and top-of-the-page overflow occur when a full line of
data has been entered from the bottom line in either mode.

[Note cursor graphic and lock-to-last-line are linked here.  The only
 sane setting is ON methinks -zben]

LOCAL-OFF
103-OFF
202-OFF
These three switches are used to select ADM-3A operation for one of the
following methods of interfacing to the computer: (1) without modems
(direct, local connection), (2) with 103-type modems, or (3) with 202-type
modems.  The appropriate switch is set (left-position) according to the
connection method used; the other two switches must be set to the OFF
position.

Setting the LOCAL switch causes line CA (Request to Send) to rise and fall
with each character transmitted.

Setting the 103 switch holds CA high, if required.

Setting the 202 switch enables 202-type operation using the secondary 
channel or turnaround code to change the direction of data over the
primary data channel (half-duplex operation).

With all three switches off, CA is held low all the time.

CODE-SEC CHAN
This switch is active only with the 202 switch (described above) in the
on position.  It is used to select the method of line turnaround for
half-duplex operation with 202-type modems.

In SEC CHAN position, enables line turn-around using the secondary channel.
202 modem operation is summarized in the Theory of Operation.

The CODE position allows line turnaround control by a turnaround code
transmitted over the primary data channel.  The turnaround code may be
either EXT [sic] or EOT, as selected by the switches described below.

EXT-OFF [sic]
EOT-OFF
One of these two switches is set to the on (left) position to select the
line turnaround code for primary channel operation with 202-type modems.
(See CODE-SEC CHAN switch description.)  With 202 and CODE selected,
one of these switches must be on and the other off; with 202 and SEC CHAN
selected, or 202 off, both the ETX and EOT switches must be set to the
OFF positions.

[Note typo - EXT should be ETX - the circuit board has it right -zben]

[202 modems were a kluge until they figured out how to stuff 1200 baud
 full duplex down a telephone line.  With today's 2400 baud modems, this
 should show you how far we have come in the last 10 years or so... -zben]


Ben Cranston
Systems Group
Computer Science Center
The University of Maryland
College Park, MD, 20742

ZBEN@UMD2.UMD.EDU
ZBEN@UMDD.BITNET
-- 
Ben Cranston  ...{seismo!umcp-cs,ihnp4!rlgvax}!cvl!umd5!zben  zben@umd2.ARPA
