DMP 400  (260-1251)               Buffer               Faxback Doc. # 4563

The DMP-400's ability to temporarily store data is one of its main 
advantages 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 printed immediately; they are stored in a separate section of mem-
ory in the Printer 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-400.

HINTS AND TIPS ON THE DMP-400 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. 
  Otherwise, the Print Head is positioned at the start of the next 
  Top-of-Form line.

* The Carriage Return code (CR = 13 decimal) automatically activates 
  printing (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.

(dtc-07/27/93)