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The problem to be solved is how to control a latched group of 8 LEDs to create a classic light chaser using MINT. In this case, the 8 LEDs are connected to a latch on port 3 of the TEC-1.
The first line is a comment
\\\\back and forward LEDs
In MINT, a comment starts with a \\ and continues all the way to the end of the line.
The first thing we need to do is write a user-defined command to take turn on the right most LED (and turn off all the others). We can do this by sending a hexadecimal 01 value to a latch on Port 3.
Let's give this command an uppercase letter D as a name (you have 26 to choose from).
:D #01 a! 7(a@ { a@#3\\> 2000()); \\\\ go left
The colon : indicates the start of a user command and must be immediately followed by D (no space). The definition continues until we reach the ;
Let's break this down further.
#01 a!
This means we initialise a variable a with 01. You have 26 general purpose variables named a..z, there are also more specialised variables \\a..\\z but we don't use those here.
Hexadecimal numbers in Mint are prefixed with #.
So #01 a ! means "take the value #01 store it in the address of variable a"
Now that a contains 01 we can look at the next part
7(a@ { a! a@#3\\> 2000())
Parentheses ( and ) indicate that this is piece of repeated code, i.e. a loop. We want to repeat the code a@ { a! a@#3\\> 2000() and we want to repeat it 7 times.
Breaking down this repeated code further we see
a@ { a!
which means fetch the value stored in variable a, shift it left one bit and then store it again in variable a (the { is the shift left operator, } is the shift right operator)
a@#3\\>
Next we want to output the value of a to the latch connected to the TEC-1's output port 3. While spaces are nearly always optional, it might be clearer if we express this code as
a@ #3 \\>
which means "with the value of a and the port address 3 do an OUT operation. \\> (not to be confused with 0) means "output"
Finally we enter a delay 2000() which is simply an empty loop iterated 2000 times. Based on our measurements of empty loops, each loop in MINT takes about 65 microseconds on a 4MHz Z80 so this delay would typically take around 1.2 seconds.
Now let's define a second user command in E
:E #80 a! 7(a@ } a@#3\\> 2000());
This works the same way as the definition D but goes in the opposite direction. #80 represents having the left-most LED turned on and } means "shift it right" on each loop
Finally we bring these two commands together and repeat them over and over.
25(DE)
While there are ways to do infinite loops in MINT in this case we only want it to repeat 25 times.