Hi Maik,
welcome to Mobiflight.
If you sign a message with Gruß, Maik, then you should talk in German. So you left you Message in the German Part of Mobiflight an the german language should be ok.
To your problems:
Mask values - here we need an excursion how to work with bits. You know, these 0 and 1.
If you add in our normal number_system (to the base of 10) 5 + 5 is the result 10. You have now not more 1 digit rather an overflow to the 2nd digit. So you add 5 + 5 is 0 overflow 1, called 10
If you add in the dual (binary) number_system (only 0 and 1) 1 + 1 you won't get 2 because this number is not possible. You have only 0 and 1! So you get 1 + 1 = 0 overflow 1, called, no, not 10 (ten), rather 1-0 (one-zero).
In the computer technology we know bits (the smallest unit), nibbles (4 bit in a row), Bytes (8 bit or 2 Nibbles), Word (16 Bit, 4 Nibbles or 2 Bytes), Double-Word (32 Bit, 8 Nibbles, 4 Bytes). Thera are also a lot of others, but these we don't need today.
If you have for example a value of 01010111 (1 Byte, two nibbles) so you can also write it as 0101 0111 for better readability.
Now you have to know that the left bit of the byte is the MSB (Most Significant Bit) and the rightest Bit is the LSB (Least Significant Bit). This ist important to know, because if you have to convert it into the decimal (our well known) number_system.
Back to our byte. This Byte can now be masked if I want to know the contents of a particular bit. Here we have to go back a little deeper into the matter.
You've probably heard the term truth table before. Masks are normally ANDed with a value.
Truth table for AND
(V1=value1, V2=value2, R=result)
V1 V2 R
0 0 0
0 1 0
1 0 0
1 1 1
As you see, only if V1 AND V2 are equal the result is 1.
This is how a mask works
Mobiflight normaly uses F or FF or FFFF or many of them as mask.
Oops, what is F. Ok, the next number_system, this time the hexadecimal number system. The base is 16. Hexadecimal is also known as sedecimal system but it's the same only another name. The abreviation is HEX
FF
HEX or 0xFF or FF
16 - all the same
How do you get to the F? The numbers 0,1,2....9 are well known, continues with A, B, C, D, E and F
Comparison of the valences DEC BIN HEX
DEC BIN HEX
00 0000 0
01 0001 1
02 0010 2
03 0011 3
04 0100 4
05 0101 5
06 0110 6
07 0111 7
08 1000 8
09 1001 9
10 1010 A
11 1011 B
12 1100 C
13 1101 D
14 1110 E
15 1111 F
Back to the mask.
Above we have the Byte 01010111, parted in nibbles 0101 0111 - would be in HEX: 5 7
Back to MF. MF masks this value with FF. But how to mask 0101 0111 with FF?
Exact,we transform FF into binary = 1111 1111
Now we link 0101 0111 with FF
0101 0111
1111 1111
The result if these values are AND-linked is
0101 0111
To check this, use the true table above bitwise.
Another calculation. We want to konow the value of the 2nd bit.
We count from right to left. 0 ist the LSB, 1 the 1st, 2 the 2nd, 3 the 3rd 4 the 4th ... and the MSB (the left one!) ist the 7th! not the 8th.
If we want the value of the 2nd bit (3rd position from right!) we have to know how the mask looks like
0101 0111
0000 0100
0000 0100 is the result because only the 3rd bit interesting and 1
The decimal result is 4 (look table above)
So you can notice: the mask for the LSB is 1, for the 2nd bit is 2, for the 3rd bit is 4, for the 4th bit is 8, for the 5th bit is 16, for the 6th bit is 32, for the 7th bit is 64 and for the 8th bit (MSB ) is 128.
Do you notice something? If you add the values together (1+2+4+8+16+32+64+128) you got 255 or 1111 1111
2 or 0xFF
So you can compare every value with any mask and get a true result.
uint16:
describes the datalength in BITs - in fact UNSIGNED
I have a small course with dual numbers in preparation, which also deals with this case, but must still be read correction.
So Maik, I hope I could help you a bit
Supporter
Code:
0892 2 Engine 1 Starter switch position (Magnetos), Jet/turbojet: 0=Off, 1=Start, 2=Gen/Alt Prop: 0=Off, 1=right, 2=Left, 3=Both, 4=Start