the first character is always the escape character
• PCL commands provide access to the printer's PCL control structure. The PCL structure controls all of the printer's features except those used for vector graphics, which are controlled by the HP-GL/2 commands.
• PCL printer commands consist of two or more characters. The first character is always the ASCII escape character, identified by the EC symbol. EC is a special control code which identifies the subsequent string of characters as a printer command. As the printer monitors incoming data from a computer, it looks for this character. When this character appears, the printer reads it and its associated characters as a command to perform and not as data to print.
PCL printer commands (other than single-character control codes) are also referred to as escape sequences. The terms printer command and escape sequence are used interchangeably throughout this manual.
Once a PCL command sets a parameter, that parameter remains set until that PCL command is repeated with a new value, or the printer is reset to its user default environment. For example, if you send the printer a command to set line spacing to 3 lines/inch, each page prints 3 lines/inch until the printer receives a different Line Spacing command, or the printer is reset.