Incremental line printer

Means for operating a printer of the dot matrix type for printing characters comprised of a first plurality of dot columns each column having a second plurality of dots;

• input latch means for receiving code words identifying a character;
• recirculating memory means having a plurality of stages each adapted to store a code word, the last stage of said recirculating memory means being the output thereof;
• output latch means for receiving and storing code words;
• means for loading a code word from said input latch means into said recirculating memory means;
• means for advancing code words in said recirculating memory means to said output of said recirculating memory means;
• means for transferring the code word in the output of said recirculating memory means into said output latch means;
• means coupled to said output latch means for printing the character whose code is stored in said output latch means and for enabling said input latch means and memory means to receive additional code words during a printing operation.

Means for operating a printer of the dot matrix type for printing characters comprised of a first plurality of dot columns, each column having a second plurality of dots, said means comprising:

• input means for receiving data code words identifying a character;
• first recirculating memory means having a plurality of stages, each said stage adapted to store a data code word, a predetermined number of said stages representing dummy positions, the remaining said stages representing data positions, the last stage of said first recirculating memory means being the output thereof;
• output latch means for receiving and storing data code words;
• means for loading a data code word from said input means into said first recirculating memory means;
• advancing means for advancing said data code words in said first recirculating memory means to said output of said first recirculating memory means;
• means for transferring a data code word in said output of said first recirculating memory means into said output latch means;
• means coupled to said output latch means for printing the character whose data code word is stored in said output latch means and enabling said input means and first recirculating memory means to receive additional data code words during a printing operation;
• second recirculating memory means having a plurality of stages equal in number to the number of stages in said first recirculating memory means, each of said plurality of stages of said second recirculating memory means being adapted to store a multi-bit status code word representative of the status of an associated stage of said first recirculating memory means, each of said status code words indicating whether its associated stage of said first recirculating memory means is a data or a dummy position and whether there is data or no data in its associated state, the last stage of said second recirculating memory means being the output thereof;
• said advancing means being coupled to said second recirculating memory means to advance status code words in said second recirculating memory means in synchronism with said first recirculating memory means;
• means responsive to a code word being loaded into said input means for loading a multi-bit status code word into said second recirculating memory means when a data code word in said output of said first recirculating memory means is loaded into said output latch means;
• means responsive to printing of a data code word in said output latch means for altering the status code word in said second recirculating memory means which is associated with said data code word in said output latch means to identify a no-data code;
• means responsive to turn-off of the printer for loading a status code word representing no data in a dummy position into a plurality of stages of said second recirculating memory means;
• bidirectional counting means coupled to the output of said second recirculating memory means for counting the number of stages in said first recirculating memory means containing data code words in either a data or a dummy position and for generating a full signal condition when a predetermined number of the stages containing data code words are counted to prevent the acceptance of further data code words from said input means.

Tab control means for line printers comprising:

• a carriage assembly reciprocally movable across a document between end points spaced apart by an amount comprised of m equispaced character intervals;
• first moving means for selectively moving said carriage in first and second opposite directions;
• a print head mounted on said carriage for printing dot columns wherein n successive dot columns collectively form a character;
• registration means having a plurality of uniformly spaced slits;
• means on said carriage for sensing said slits to generate pulses when said carriage moves in either direction;
• recirculating memory means having m stages each adapted to store a code word representing a tab, no tab or end of line condition, said recirculating memory means having an output stage;
• second memory means responsive to said sensing means for moving the contents stored in said stages of said recirculating memory means in a first direction as said carriage moves in said first direction;
• means responsive to a tab set input for loading a tab code into the stage of said recirculating memory means associated with the position of the print head at the time said tab set input is received;
• second means responsive to a tab input for moving said carriage in said first direction at a slew rate, whereby said sensing means advances the contents in said recirculating memory means in synchronism with the movement of said carriage;
• means responsive to the presence of a tab code at said output stage of said recirculating memory means for stopping said carriage, whereupon said first moving means controls movement of said carriage at the print rate.

A printer having:

• head means for printing dot matrix type patterns;
• means for selectively moving said head means in the forward or reverse direction;
• first multi-stage recirculating memory means for storing data codes representing patterns to be printed and for storing function codes;
• means coupled to the output of said first recirculating means for converting data codes into pattern signals coupled to said head means;
• means responsive to printing of a pattern for advancing the data in said first memory means by one stage;
• registration means responsive to movement of said head means for generating registration signals;
• up/down counter means;
• means for monitoring the direction of movement of said head means;
• means for generating an enabling signal whenever the output stage of said memory means is empty;
• said up/down counter means being responsive to said enabling means and said registration means for being incremented or decremented whenever said head means is moving in respectively the forward or reverse direction and is not printing;
• means for halting the print head means at least a predetermined distance from the last printed pattern;
• means responsive to a backspace code in the output of said memory means for incrementing said up/down counter means by one count;
• means for enabling said print head means to print patterns only when said up/down counter means reaches a zero count whereby the last printed character is printed over whenever backspace code has been received.