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Graphtrax II
Chapter 5
Graphtrax II
Caution
- Entering High Resolution Space
To create graphics on the MX-70, we must enter a completely new mode: the
GRAPHICS MODE. In this mode, pre-defined characters do not exist - only
dots. We create our own characters or images by arranging the dots however
we wish.
In the GRAPHICS mode we have complete control over which pins fire, and
when. It sounds like a lot of fun, and is, but there are an awful lot of dots in just
one line, let alone an entire page.
Think of it this way. There are 80 “regular” characters in a normal line (row).
Each character is 6 dots wide (5 dots plus 1 blank column). That comes to 480
columns in each row. Good grief!
Fortunately, we don’t have to fill all 480 columns on every line. In fact, the first
thing we do when entering graphics mode is tell the printer how many columns
of dots we will send it, a row at a time.
Warp 3
The graphics mode is entered by sending the printer a cluster or sequence of 3
codes:
FORMAT:
<ESC> "K"
N1
N2
-----------
---------- -------
EXAMPLE:
CHR$ (27) "K" CHR$ (15)
CHR$ (0)
CHR$ (27) is of course the Escape code, and Escape “K” means KICK
into graphics mode.
CHR$ (15) says: “reserve 15 columns for graphics.” N1 can range from 0
to 255 (O-127 for 7 bit computers)
CHR$ (0) If N2 is 0, it means
“Ignore me, N1 specifies the number of
columns to expect.”
If N2 is 1, the number of columns will equal N1 + 256. If this
sum of N1 and N2 exceeds 480, only 480 columns will be
reserved.
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