The Cursor Y Position on CR

If the next byte to display is CR, then cursor y position is incremented by 1. More formally,

When we press the "Enter" key, We want the display to move to the beginning of the next line. When we press the "Enter" key, the keyboard sets memory cell #8 to 13, which is the "carriage return" or "CR." When the display sees 13 in memory, it will increment cursor y by 1 as long as cursor y is not yet on the last line.

For example, suppose the following are true:

• value of cell 27 at time 71 = 1
• number of characters read at 71 = 0
• value of cell 10 at time 71 = 13
• cursor y at time 71 = 0

Since the display hasn't read any characters yet, the next cell to read from is 10 + 0, or 10. And the value of cell #10 is 13. Also, the cursor y value is 0, which is less than 11. Thus, we conclude that:

cursor y at time (71 + 1) = (cursor y at time 71) + 1

Which simplifes to:

cursor y at time 72 = 1

see here for the full proof.

Try running the simulator below and click on the "Enter" key to see the cursor y value increase.

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