Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

76 Chapter3

Common Device Control Functions

Writing to Asynchronous Devices

Sending Escape Sequences

You can also use FWRITE to send escape sequences to an asynchronous

device. Escape sequences can be used to alter the physical settings of a

device. For example, on most supported terminals you can use escape

sequences to set terminal straps, control the placement of the cursor on

a terminal screen, and set margins. You should consult the manual for

your device for a summary of useful escape sequences.

In the following example the variable

esc_seq

contains the string

’ESC&s1D’

. This escape sequence selects page block mode at the

terminal (opens the “D” strap). The escape sequence can be sent to the

device with the following FWRITE call:

FWRITE(file_num, esc_seq, -5, octal(‘320’));

The length parameter is speciﬁed as 5 bytes, the length of the escape

sequence (ESC is one byte). Carriage control is set to %320, so that no

carriage return or linefeed are sent. As a result of this call, the terminal

on which the ﬁle speciﬁed by file_num is opened will be strapped for

page block mode.

Using PRINT

In much the same way that READ and READX provide a quick method

for reading from the standard input device, PRINT provides a quick

method for writing to the standard output device. PRINT sends a string

of ASCII characters to $STDLIST. The syntax of the call is as follows:

CAI 16V I16V

PRINT(message,length,controlcode);

The message parameter is a character array that holds the string to be

written to the device. It must begin on a halfword boundary, as must all

character arrays.

The length parameter speciﬁes the length of the character string. If

the length of the message exceeds the conﬁgured record length of the

terminal, successive records will be written.

The controlcode parameter speciﬁes the carriage control to be applied

when the message is output. Either a 0, 1, or one of the valid carriage

control directives should be passed in this parameter. See the

discussion of the FWRITE intrinsic for more information on

controlcode values.

Like READ and READX, PRINT has a number of limitations on the

way it can be used. Because no ﬁle number is available, :FILE

commands are not useful, nor is it possible to use the FCHECK

intrinsic to check error conditions. For permanent programs it is

recommended that FWRITE be used instead.