Control Functions

Introduction
Control Function Notation
Single-Character Control Functions
Recognized C0 (7-Bit) Control Characters
Recognized C1 (8-Bit) Control Characters
Multiple Control Functions

Introduction

Control functions cause Verastream to perform certain actions, such as move the text cursor, add a line of text, assign character attributes, and change character sets. Typically, the host application sends control functions to Verastream to perform the desired actions. There are three symbols used in this section that describe a sequence:

ESC: Stands for the Escape character, and begins an escape sequence.
CSI: Stands for the Control Sequence Introduction character. When Verastream receives this character, it recognizes the string that follows as a control sequence.
DCS: Stands for the Device Control String character, and begins a device control sequence.

Control Function Notation

The following notation is used throughout this section:

Most control functions have a mnemonic identifier. You will never need to enter the mnemonic; it’s simply a convenient word to help you remember the name of the control function. For example, DECCOLM is the Digital mnemonic for setting the number of display columns.
Control functions are case sensitive, and must be typed exactly as shown.
Where appropriate, a slash is used through a zero (Ø) to distinguish it from the uppercase letter O.
Note the difference between a lowercase L (l) and the number 1 (1).
References are occasionally given to a character’s decimal value in the character set charts. For example, the space character is ASCII decimal 32 (see the figure on page 252). Control characters are always in the same positions in the charts, and can be located uniquely by their decimal value; the word “ASCII” is omitted.
This topic shows control functions in their 8-bit format. You can always use the 7-bit equivalent escape sequence to represent the 8-bit control, as shown in the Recognized C0 (7-Bit) Control Characters Table.
Parameters you supply for a sequence are enclosed in angle brackets. For example, when using the CSI<n>C control function, replace <n> with the number of spaces you want the cursor to move. If <n> is omitted, the default is used. For most sequences, the default is 1 (when there is not a corresponding Ø sequence).
Numeric parameters are represented by ASCII strings. For example, in the sequence CSI10;13H the numbers are the strings 10 and 13,
not the decimal values 10 (LF character) and 13 (CR character). Numeric parameters are constrained to the range 0–9999, inclusive. Any numeric parameter with a value greater than 9999 is interpreted as 9999. The plus sign (ASCII decimal 43) and the minus sign (ASCII decimal 45) are not within the range of legal control characters. Therefore, signed numbers, for example “+10” or “-12,” cause a control sequence or a device control string to be rejected. Do not include signs with numeric parameters.

Single-Character Control Functions

A single-character control function is made up of one control character (in contrast to multiple-character control functions). There are two sets of single-character control functions available on VT200, VT300, and VT400 terminals:

C0 control characters have decimal values 0–31. Verastream supports only the C0 characters shown in the Recognized C0 (7-Bit) Control Characters Table. Each C0 character is encoded in 7 data bits, with the high-order bit always 0. C0 codes, therefore, can be used in both 7-bit and 8-bit operating environments. LF and CR, for example, are single-character C0 control functions.
C1 control characters have decimal values 128–159. Verastream supports only the C1 characters shown in the Recognized C1 (8-Bit) Control Characters Table. Each C1 character is encoded in 8 data bits, with the high-order bit always 1. C1 characters provide a few more functions than C0 characters, but can only be used directly in an 8-bit operating environment. DCS, for example, is a single-character C1 control function.

In 7-bit operating environments, C1 characters must be converted to a two-character escape sequence equivalent.

Recognized C0 (7-Bit) Control Characters

The following table lists the C0 control characters that Verastream recognizes. C0 controls can be used in both 7-bit and 8-bit environments. To represent C0 controls in a Verastream macro, use the Chr$(<n>) syntax, where <n> is the decimal value of the C0 control. See the “Decimal” column in the following table:

Name	Character	Octal	Keystroke	Action
Null	NUL	0	^@	Ignored when received
Enquiry	ENQ	5	^E	Transmits the answerback message
Bell	BEL	7	^G	Sounds a bell
Backspace	BS	10	^H	Moves cursor left one position on the current line
Horizontal tab	HT	11	^I	Moves cursor to the next tab stop, or to the right margin.
Linefeed	LF	12	^J	Causes a linefeed or new line operation.
Vertical tab	VT	13	^K	Same as linefeed
Form feed	FF	14	^L	Same as linefeed
Carriage return	CR	15	^M	Moves the cursor to the left margin of the current line
Shift out (locking shift 1)	SO	16	^N	Maps the G1 character set into GL. G1 is designated by using a Select Character Set (SCS) sequence.
Shift in (locking shift 0)	SI	17	^O	Maps the G0 character set into GL. G0 is designated by using a Select Character Set (SCS) sequence.
Device control 1 (XON)	DC1	21	^Q	Continues sending characters when transmit is set to Xon/Xoff.
Device control 3 (XOFF)	DC3	23	^S	Stops sending characters when transmit is set to Xon/Xoff.
Cancel	CAN	30	^X	Cancels the sequence when received during an escape or control sequence.
Substitute	SUB	32	^Z	Same as cancel;displays a backwards question mark.
Escape	ESC	33	^[	Introduces an escape sequence and cancels any escape sequence or control sequence in progress.
Delete	DEL	177	(none)	Ignored when received.

Recognized C1 (8-Bit) Control Characters

In 8-bit environments, C1 controls can be sent directly. In a 7-bit environment, you can send an 8-bit C1 control character by converting it to an equivalent 7-bit escape sequence. The 8-bit controls are single character codes (such as CSI), whereas their 7-bit equivalents are two-character sequences (such as ESC[).

To form an equivalent 7-bit escape sequence from an 8-bit control character:

Subtract the hexadecimal value 40 from the C1 control code’s value.
Precede the result with the ESC character.

For example, the IND character (decimal 132) has a hexadecimal value of 84. To convert IND to a 7-bit equivalent, first subtract hexadecimal 40:
84 hex - 40 hex = 44 hex. Hexadecimal 44 is the letter D. Therefore, to represent the IND character in a 7-bit environment, you would use ESCD.

The following table lists the C1 control characters that Verastream recognizes:

Multiple-Character Control Functions

The C0 and C1 codes listed in the Recognized C0 (7-Bit) Control Characters and Recognized C1 (8-Bit) Control Characters tables are single-character control functions, performing simple functions.

Multiple-character control functions, in contrast, can perform many more functions than the C0 and C1 controls, and are formed by a sequence of characters. There are three types of multiple-character control functions, introduced by the following single-character C0 and C1 controls:

Escape sequences, introduced by the ESC character
Control sequences, introduced by the CSI character
Device control strings, introduced by the DCS character

Multiple-character control functions include both control characters and normal ASCII text, such as letters, numbers, and punctuation. For example, the multiple character device control string DCSØ!u%5ST assigns a user-preferred supplemental character set.

Escape Sequences

An escape sequence begins with the C0 character ESC (decimal 27). To enter the ESC character in the Design Tool, press the ESC key. After receiving an ESC character, Verastream interprets the next characters as part of the sequence.

Control Sequences

A control sequence begins with the C1 control character CSI (decimal 155). To enter the CSI character in the Design Tool, press the ESC key plus the [ key.

Control sequences usually include variable parameters. The format is:

CSI P...P I...I F

P...P	Zero or more parameters. You can have up to 16 parameters per sequence, using a semicolon (;) to separate each one.
I...I	Zero or more intermediate characters.
F	The final character indicating the end of the control sequence.

For example, the following control sequence sets the scrolling region, where the top margin is at line 7 and the bottom margin is at line 18:

CSI7;18r

In this example, 7 and 18 are the parameters and r is the final character. This sequence does not have any intermediate characters.

Device Control Strings

A device control string begins with the C1 control character DCS (decimal 144). To enter the CSI character in the Design Tool, press the ESC key plus the P key. Device control strings always include a data string. The format is:

DCS P...P I...I F <data string> ST

P...P	Zero or more parameters. You can have up to 16 parameters per sequence, using a semicolon (;) to separate each one.
I...I	Zero or more intermediate characters.
F	The final character indicating the end of the device control string.
<data string>	A data string of zero or more characters. Use a semicolon (;) to separate individual strings. The particular range of characters included in a data string is determined by the individual device control string. Any character except ST (decimal 156) can be included in a data string.
ST	The string terminator. Type Chr$(27)& "Ë for 7-bit mode, or Chr$(156) for the 8-bit equivalent. (You can also press e-\ in the terminal window.)

APC, OSC, and PM

The application program command (APC), operating system command (OSC), and privacy message (PM) are also C1 controls. However, VT terminals—and Verastream—ignore them. The controls have the same format as device control strings and end with an ST. When Verastream receives an APC, OSC, or PM introducer, it discards all following characters until receiving a string terminator (so the whole sequence is discarded).

Interrupting Control Sequences

You can use the following C0 control characters to interrupt a control function or recover from an error:

ESC	Cancels a sequence in progress, and begins a new sequence.
CAN	Cancels a sequence in progress. Verastream interprets the characters that follow the CAN character as usual.
SUB	Same as CAN, except displays a backwards question mark.