Apple Orchard 1980 Fall v1n2 reduced

FALL 1980 THE A PPLE ORCHA RD PAGE 13
Before we get started with the experiments, I must tell you
that the screen looks at the binary bits backwards from the way
you use them in counting. What this means is that the left most
bit is valued at 1 and the right most bit is valued at 128. Also,
only 7 bits will show up on the screen. I am told that the 8th bit
controls the additional colors on the newer machines. My APPLE
is #86 and does not have the mod, so I have never used the 8th
bit. Hopefully, someone out there who has extensive experience
with the colors will submit a subsequent article.
At this point, you should be looking at the blank Hi-res
screen. Memory location 8192 is the one that controls the first
7 dots in the upper left corner of the screen. So, POKE a 1 into
8192 by typing 'POKE 8192,1' and hit return. One dot in the
A -
B
A 1 024 0
B 1152 1
c 1280 2
D 1408 3
1536 4
1664 5
1792 6
1920 7
1064 8
11 92 9
1320 10
1448 11
1576 12
1704 13
1832 14
1960 15
1104 16
1232 17
1360 18
1488 1 9
1616 20
1744 21
1872 22
2000 23
CHART #1
corn er should have come o n. Now type 'POKE 8192,64 '. The dot
that was on should have gone off and another one come on.
That's because 64 is the value of the 7th bit, which is the last bit
that the graphics will use. If you want both dots on at the same
time, add the 2 values together, 64+1=65, and type 'POKE 8192,
65'. Now, both dots should be on. This probably seems like a lot
of work to get something on the screen. It is, if you do it all manually.
However, when you can use formulas to figure out where
to put the dots, the computer will do it all for you. Play with that
for awhile. You can use any RAM location between 8192 and
8231 for the enti re top line.
Now that you know how to control each RAM location, let's
talk about the formatting of the screen so you can use the whole
thing.
D
c
0 1063
3 11 91
6 1 31 9
9 1447
1 2 1575
1 5 1703
1 8 1831
21 1959
1 11 03
4 1231
7 1359
10 1487
13 1615
16 1743
1 9 1871
22 1999
2 1143
5 1271
8 1399
11 1527
14 1655
17 1783
20 1911
23 2039
This chart represents the screen as you see it in the text mode, with characters on it. It is broken into a lot of little boxes, (40 across
and 24 down). Only one character at a time can be in each box. Notice the 'A' in the upper left corner It will be on all the other charts
also. This will help you to keep proper perspective as to the size of the portion of screen that we are looking at. In the text mode it takes
only one memory location to operate each one of these boxes. In Hi-res it takes 8 bytes of RAM to control each box. Unfortunately the
RAM locations do not follow through from one line to the next. In this chart you see 4 columns of figures. They are:
A- The first RAM location used for that line in the text mode.
B- The screen line number.
C- The line numbers as they fall in sequential RAM locations.
D- The last RAM location used for that line.
The screen line# will be the one referred to from this point unless otherwise noted.
Notice that line #1 's first RAM location is 1024 and that the last is 1063. That is a total of 40 RAM locations for the 40 characters
across on the first line. Also notice that line #2 does not have the next RAM location of 1064. It is on line #9. So, if following the RAM
in sequence, it jumps to line #9 from line #1. The last RAM location on line 9 is 1103. 1104 is the first RAM location on line 17. The
last RAM location of line 17 is 1143. Now, here is a more confusing part. There are 8 RAM locations that are not used ( 1144-1151 ).
1152 starts line #2. This continues until the entire screen is filled.