DMP 420 (260-1267) Buffer Faxback Doc. # 4637 The DMP-420's ability to temporarily store data is one of its main advant- ages over a typewriter. Codes sent to a typewriter (i.e., keys pressed) are transferred immediately to the paper. Codes sent to a Printer are not print- ed immediately; they are stored in a separate section of memory in the Print- er called the buffer. When the buffer fills, or certain codes are received (e.g., LF or CR), the buffer is emptied and all data is printed on the paper. What happens after the buffer data is printed depends on the circumstances. In some cases, printing continues on the same line; in others, the Print Head is moved to a different position relative to the paper. In the DP mode, commands for changing print fonts, Line Feed, etc., can be stored in the buffer to take affect when the data is dumped to paper. Understanding how the buffer works is important for those who wish to gain full control of the DMP-420. HINTS AND TIPS ON THE DMP-420 BUFFER... For DP, WP, and Graphics Modes * The buffer allocates a fixed number of dots depending on the character width selected. The buffer is emptied when the data stored equals that number. Printing resumes at the start of the next line unless Switch #6 is set the CR only. If different character widths have been used on the same line, the last character added may exceed the dot count. the buffer is printed without this last character. * The last character received by the buffer is printed at the start of the next print line following an automatic Line Feed and Carriage Return. * The Form Feed code (FF = 12 decimal) automatically activates printing (if the code makes it to the Printer). If LF only has been selected (Switch #5), then the buffer is printed and the print head moves to the next Top- of-Form line without a carriage return to the start of the line. Other- wise, the Print Head is positioned at the start of the next Top-of-Form line. * The Carriage Return code (CR = 13 decimal) automatically activates print- ing (assuming at least one character code is already in the buffer). If Carriage Return only has been selected via hardware, the Print Head is moved to the start of the current line and the next buffer full will print over the current line. Otherwise, subsequent characters will be printed at the start of the next print line. * The Line Feed code (LF = 10) automatically activates printing. If LF only has been selected (Switch #5), then the buffer is printed and the Print Head moves to the next print line without a carriage return to the start of the next line. Otherwise, the Print Head is positioned at the start of the next print line. * If the computer delays more than a second before sending the next print code, the buffer is printed. Printing continues from the current position. * The Head Positioning sequence (27 16 n1 n2) prints the buffer. Printing continues in the current line at the dot address specified by the (27 16) command. DATA AND WORD PROCESSING MODES ONLY: * The backspace command activates printing. Printing continues in the cur- rent line at the dot address specified by the command. * If a character set of different dot density is selected, the data in the buffer is printed. Codes for changing character sets are: 27 17, 27 18, 27 19, 27 20, 27 23. Printing continues in the current line with the new character style. * Dot graphics printing continues from the current character position. * When a start Bold or end Bold is received, the buffer is printed. * Bold printing continues from the current character position. GRAPHICS MODE ONLY: * When the end Graphics Mode command is received, the Printer returns to the previous print mode and printing continues in the same line from the current print position. NOTE 1: In the description, "next line" means the new line performed by a Line Feed operation. In Data Processing Mode, if a Reverse Line Feed has been set in the memory, the Line Feed operation will cause paper to move in the reverse direction. NOTE 2: Repeat data can cause a buffer full condition, as well as an over- flow by single characters. HEX PRINT MODE * The DMP-420 is capable of printing hexadecimal values for data that is transmitted to it. "Hex Print Mode" is useful for checking exactly what information is being received by the Printer. * To implement this function, turn on the power to the Printer while simultaneously holding down the ON-LINE, FORM FEED, LINE FEED, 1/2 FORWARD LINE FEED and 1/12 REVERSE LINE FEED buttons. * Before printing, be sure that 15 1/2" paper is loaded in the Printer to avoid printing on the platen. Then press the ON-LINE button and run the program that you want to check. (smm 07/27/93)