Specifications

CHAPTER 7
TELETYPE (MODEL LT33-DC/DD)
The standard Teletype Model 33 ASR (Automatic Send-Receive) can be used
to type in or print out information at a rate of up to ten characters per sec-
ond, or to read in or punch out perforated paper tape at a ten characters
per second rate. Signals transferred between the 33 ASR and the control
logic are standard serial, 11-unit code Teletype signals. The signals consist
of “marks” and “spaces” which correspond to idle and bias current in the
Teletype serial line, and to O’s and l’s in the control and computer. The
start mark and subsequent eight bits are each one unit of time duration and
are followed by the stop mark which is two units.
The 8-bit-code used by the Model 33 ASR Teletype unit is the America1
Standard Code for Information Interchange (ASCII) modified. To convert the
ASCII code to Teletype code, add 200 octal (ASCII + 200s = Teletype).
The Model 33 ASR can generate all assigned codes except 340 through
374 and 376. The Model 33 ASR can detect all characters, but does not
interpret all codes that it can generate as commands. The standard number
of characters printed per line is 72. The sequence for proceeding to the next
line is a carriage return followed by a line feed. Punched tape format is as
follows:
Tape Channel
Binary Code
(Punch = 1)
87 654 S 321
10 110 100
Octal Code
2 6 4
(S = Sprocket)
SIZE- Floor space approximately 221/” wide, 181/2” deep
Cable length 8 feet
MODEL POWER REQUIREMENTS
LT33-DC
115 v 510% 60 kO.45 Hz
LT33-DD 230 V -t-iO% 50 kO.75 Hz
TELETYPE CONTROL (MODEL KLll)
TELETYPE CONTROL-Serial information read or written by a Teletype unit
is assembled or disassembled by the control for parallel transfer on the
Unibus. The control also provides the flags which cause a priority interrupt
and indicate the availability of the teletype.
KEYBOARD/READER-The Teletype control contains an 8-bit buffer (TKB)
which assembles and holds the code ‘for the last character struck on the
keyboard or read from the tape. Teletype characters from the keyboard/
reader are received serially by the 8-bit -shift register TKB. The code of -a
Teletype character is loaded into the TKB so that “spaces” correspond to
binary O’s and holes, “marks,” correspond to binary 1’s. Upon program
command, the contents of the TKB may be transferred in parallel to a
memory location or a general register.
A character is read from the low-speed reader by setting the Teletype reader
enable bit, (RDR ENB), to a 1. This sets the busy bit (BUSY) to a 1. When a
Teletype character starts to enter, the control de-energizes a relay in the
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