Filter
Top Products
Graphtrax II
Now for the Bad News
Before racing off to create a HI-RES forgery of the Mona Lisa, be aware that
the above is how is it SUPPOSED to work. Reality is brutal - there are some
exceptions to almost every rule.
Code numbers 9 and 13 for the Apple, and 0, 10, 11, and 12 for the TRS-80 create
havoc when used as N1 or N2. (It’s deja vu from the last chapter). Other
computers may have trouble with different codes. Even worse, the printer
accepts code numbers from 0 to 255 to determine the dot pattern, but many
computers are not able to send code numbers greater than 127. It’s the old
“missing eighth bit” caper. Like the “lost chord.”
Sigh! Once again the printer can out perform a computer. In the Apple’s case,
the Epson Parallel Interface card deactivates the eighth bit so Apple users can
control only 7 pins. If it didn’t, bit 8 from the Apple would be on all the time,
firing pin 8 every time. Most TRS-80s can control all 8 pins without difficulty.
Back to the Welcome Program
We’ve seen that each pin is associated with a number. The numbers 1, 2, 4, 8,
16, 32, 64, I28 all relate to the mathematical powers of 2. Binary math, and all
that stuff. Here’s the relationship:
2
7
=
128
2
6
=
64
2
5
=
32
2
4
=
16
2
3
=
8
2
2
=
4
2
1
=2
2
0
=
1
Let’s see if we can fire the pins, in sequence, from the bottom up. Make the
program read:
9 PR #1
(Apple)
10 PRINT CHR$ (27) “K” CHR$ (50) CHR$ (0) ;
20
FOR
P =
0 TO 6
30 PRINT CHR$ (2^P) ;
40
NEXT
P
50
GOT0
20
45