Expert: Alex Barry - 6/12/2009

Question
I have no clue on how to do this RAM program.
Write a program that lets the LED turn on one a time (15 leds) in chronological order and then go backwards. Therefore 15 locations need to be wirtten to and read from. the program must run in a loop.
a sample how the ram works
Out 890, 9 XOR 11
Out 890, 13 XOR 11
Out 890, 9 XOR 11
Out 888, 2^0
Out 890,8 XOR 11
Out 890, 9 XOR 11
Out 890, 11 XOR 11
Out 890, 9 XOR 11


Answer
Hi, Jon,

I haven't tinkered with this sort of thing (LEDs...probably through the parallel port?), but I think I can guide you in the right direction

Right now, I'm assuming that the code given lights up 1 of the LEDs.

So, I'm going to assume this:
1. the first 3 OUT 890 statments prepare the LED
2. the out 888 selects the particular LED you want
3. The remaining OUT statements reset the system for the next LED

If this is true, this will probably work:

declare sub toggleLED( n as integer )

dim i as integer
' Turn on LEDs
for i = 1 to 15
 toggleLED( i )
next i
' Turn off LEDs in reverse
for i = 15 to 1 STEP -1
 toggleLED( i )
next i
end 0

sub toggleLED( n as integer )
 DIM id AS INTEGER
 id = n - 1
 Out 890, 9 XOR 11
 Out 890, 13 XOR 11
 Out 890, 9 XOR 11
 Out 888, 2^( id )
 Out 890,8 XOR 11
 Out 890, 9 XOR 11
 Out 890, 11 XOR 11
 Out 890, 9 XOR 11
end sub

CAUTION: before you test that code out, have your teacher double check it.  With an improper OUT statement, it can either buffer up the parallel port, or the whole computer.  It is very important to double check all any OUT statement code.

If that doesn't help you out, on this section of allexperts, Don may be able to help you more - I'm pretty sure he's had more experience in this area than myself.

Hope that points you in the right direction,
-Alex