• RS-232 & Serial Signalling
• ASCII Tables
• ITA2 Tables
• Model 28 Teletype Typebox

RS-232 DB-25 Earth 1 14 TXD 2 15 RXD 3 16 RTS 4 17 CTS 5 18 DSR 6 19 GND 7 20 DTR DCD 8 21 9 22 RI 10 23 11 24 12 25 13

RS-232 DE-9 DCD 1 6 DSR RXD 2 7 RTS TXD 3 8 CTS DTR 4 9 RI GND 5

Connectors as viewed from front of female connector or rear of male connector.

In standard asynchronous serial communications the LSB is sent first.

In standard asynchronous serial communications the idle state is Data-1/Mark.

Signalling Levels

Data	Telecom	RS-232 Data	Current Loop
0	Space	+3 to +15 V	Open circuit / no current
1	Mark	-3 to -15 V	Closed circuit / current flow

Binary	Control	RS-232 Control
0	Not Asserted	-3 to -15 V
1	Asserted	+3 to +15 V

ITA2 is the standard code used by 5-level teletypes such as the Model 28.

ITA2 is frequently referred to as Baudot code. They are both 5-level codes, however the encodings are actually different.

The standard US Teleprinter code varies from ITA2 in several of the Figures characters. These are shown in the US Figures column - the differences are shown, an empty entry in the column implies the same as ITA2 Figures.

• SP = blank space
• CR = Carriage Return
• LF = Line Feed
• NUL = no action
• BEL = ring the bell
• LTR = shift to Letters state
• FIG = shift to Figures state
• AB = send Answerback message
• UD = user-defined

See for ref: Five-unit codes at www.rtty.com

(Local Note: the military 28 is setup for the US code, the beige 28 is ITA2 with some US figures as per ? Figures column).

The table shows the code values for the Model 28 Teletype typebox matrix, along with the symbol placement for the US-ITA2 character code. This is as viewed from the front of the teletype, and hence looking at the rear of the typebox.

Bits can be labeled in terms of their binary weighting in the code or the time sequence of transmission: bit 2^0 is the 1st sent (t1) while 2^4 is the last sent (t5).

• The typebox is effectively two 4*8 matrices aligned horizontally. One matrix is for the Letters shift state, the other for Figures shift state.
• Bits 2^0 (t1) and 2^1 (t2) select 1 of 4 vertical positions of the typebox.
• Bit 2^2 (t3) determines a leftward or rightward horizontal motion of the typebox from the 'home' position between the 0 and 4 columns.
• Bits 2^3 (t4) and 2^4 (t5) determine 1 of 4 positions on the left or right side in mirror-image from home.