The End Block box contains the command which terminates or ends the processing of a block of graphics data.
The Diconix 150 Plus printer stops processing graphics data at the conclusion of the command specified in the Send Block box; therefore, the End Block box is empty.
The HP LaserJet IIP printer processes a single block (or row) of data at a time; therefore it was not necessary to enter a command to terminate the processing of graphics data, and the End Block box is empty.