An Introduction to Dot Matrix Printing

Line 10 contains the following 2 distinct commands:

1.An <ESC> “A.” It opens Pandora’s box to let us set the vertical line spacing accurate to a single DOT - 1/72nd of an inch. Mercy!

2.A CHR$ (##). We can specify how many dots we wish to roll down between the top of one line’s printing and the top of the next. The number can range from 0 to 85. We picked 12, since that is the default mode. TRS-80 fans and some others may have to use CHR$ (#+ 128) just to be on the safe side.

Whatever new line spacing we specify is in effect as soon as line 10 is received by the printer.

To dramatically illustrate the possibilities this feature opens up: DELETE lines

30 and 40, and change the following lines:

5

S

= l

' 1 DOT

(TRS use S= 129)

9

PR

#1

 

(Apple)

10PRINT CHR$ (27) "A" CHR$ (S)

20

PRINT

"LINE ONE",S

(TRS use S-128)

49

S = S

+ 1 : GOT0 10

 

Line 5 starts us off with a dot spacing of l/72”.

Line 10 brings in the dot number “S” as a variable.

Line 20 prints the dot spacing in 72nds of an inch.

Line 49 adds 1 to the dot spacing, and we do it all again.

RUN until the dot spacing reaches at least 24, then <CTRL-C> or <BREAK>

to stop execution.

 

 

WOW!

 

 

 

But What do it Mean, Boss?

Well, Rochester, it’s like this.

Where the number “1” is printed, the tops of the lines are only one DOT apart

(l/72”), instead of the usual 12 dots. That’s why the letters are printed all over

" W E L L

ROCHESTER."

each other.

 

3 5