Testing Conditions on Port Bytes - ignoring certain bits?
up vote
3
down vote
favorite
Being new to testing byte and bit conditions, I feel like there has to be a better way to test for conditions/values on a byte (read from a port).
For example, I'm reading 8 bits from PORTK. I need to test for a pattern of high bits. (Say, byte value of 207 - bits 7, 6, 3, 2, 1, 0 all high.) Bits 4 and 5 I don't care about. They CAN be high, or can be low. (Using datasheet terminology, they're "X - Don't Care".)
I could do an if, and test if the value equals 207, 223, 239, or 255, but that seems messy and like there would be an easier (and cleaner to read) way.
Edit to add: I've looked at Bit Operators, and .. something is telling me I should/could be using one of those. But I'm having a difficult time walking through which one would help me.
Thanks!
-Mike
arduino-mega bit
asked 15 hours ago
Coyttl
184
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Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
up vote
3
down vote
favorite
Being new to testing byte and bit conditions, I feel like there has to be a better way to test for conditions/values on a byte (read from a port).
For example, I'm reading 8 bits from PORTK. I need to test for a pattern of high bits. (Say, byte value of 207 - bits 7, 6, 3, 2, 1, 0 all high.) Bits 4 and 5 I don't care about. They CAN be high, or can be low. (Using datasheet terminology, they're "X - Don't Care".)
I could do an if, and test if the value equals 207, 223, 239, or 255, but that seems messy and like there would be an easier (and cleaner to read) way.
Edit to add: I've looked at Bit Operators, and .. something is telling me I should/could be using one of those. But I'm having a difficult time walking through which one would help me.
Thanks!
-Mike
arduino-mega bit
asked 15 hours ago
Coyttl
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
up vote
3
down vote
favorite
up vote
3
down vote
favorite
Being new to testing byte and bit conditions, I feel like there has to be a better way to test for conditions/values on a byte (read from a port).
For example, I'm reading 8 bits from PORTK. I need to test for a pattern of high bits. (Say, byte value of 207 - bits 7, 6, 3, 2, 1, 0 all high.) Bits 4 and 5 I don't care about. They CAN be high, or can be low. (Using datasheet terminology, they're "X - Don't Care".)
I could do an if, and test if the value equals 207, 223, 239, or 255, but that seems messy and like there would be an easier (and cleaner to read) way.
Edit to add: I've looked at Bit Operators, and .. something is telling me I should/could be using one of those. But I'm having a difficult time walking through which one would help me.
Thanks!
-Mike
arduino-mega bit
asked 15 hours ago
Coyttl
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Being new to testing byte and bit conditions, I feel like there has to be a better way to test for conditions/values on a byte (read from a port).
For example, I'm reading 8 bits from PORTK. I need to test for a pattern of high bits. (Say, byte value of 207 - bits 7, 6, 3, 2, 1, 0 all high.) Bits 4 and 5 I don't care about. They CAN be high, or can be low. (Using datasheet terminology, they're "X - Don't Care".)
I could do an if, and test if the value equals 207, 223, 239, or 255, but that seems messy and like there would be an easier (and cleaner to read) way.
Edit to add: I've looked at Bit Operators, and .. something is telling me I should/could be using one of those. But I'm having a difficult time walking through which one would help me.
Thanks!
-Mike
arduino-mega bit
arduino-mega bit
asked 15 hours ago
Coyttl
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 15 hours ago
Coyttl
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 15 hours ago
Coyttl
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 15 hours ago
Coyttl
184
asked 15 hours ago
Coyttl
184
184
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Coyttl is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
up vote
6
down vote
accepted
You need to use boolean arithmetic. Use the AND operator (&) to combine the incoming value AND the "mask" value (the value of the bits you do care about) and see if it equals the mask bit:
byte wanted = 0b11001110; // 207
byte incoming = 223; // for example 11011111
if ((wanted & incoming) == wanted) {
// whatever
}
The AND operator compares each bit of the bytes in turn. If they are BOTH 1 then the result is 1. Otherwise the result is 0. So the above gives:
wanted: 11001110
incoming: 11011111
AND: 11001110
And the result matches "wanted". If you had some other value for incoming it could look like this:
wanted: 11001110
incoming: 01011011
AND: 01001010
And you can see that the result doesn't match.
answered 15 hours ago
Majenko♦
65.8k42874
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
That is correct.
– Majenko♦
11 hours ago
add a comment |
up vote
2
down vote
There are ways to mask off the don't care bits.
Say your example, 0b11xx1111.
Then
incomingByte = Serial.read();
incomingByte = incomingByte || 0b00110000; // make 4, 5 high
if (incomingByte == 0b11111111){
// got all 1s, do something
}
else {
// some 0s received, do something else
}
edited 11 hours ago
Juraj
6,4102925
answered 13 hours ago
CrossRoads
9637
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
6
down vote
accepted
You need to use boolean arithmetic. Use the AND operator (&) to combine the incoming value AND the "mask" value (the value of the bits you do care about) and see if it equals the mask bit:
byte wanted = 0b11001110; // 207
byte incoming = 223; // for example 11011111
if ((wanted & incoming) == wanted) {
// whatever
}
The AND operator compares each bit of the bytes in turn. If they are BOTH 1 then the result is 1. Otherwise the result is 0. So the above gives:
wanted: 11001110
incoming: 11011111
AND: 11001110
And the result matches "wanted". If you had some other value for incoming it could look like this:
wanted: 11001110
incoming: 01011011
AND: 01001010
And you can see that the result doesn't match.
answered 15 hours ago
Majenko♦
65.8k42874
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
That is correct.
– Majenko♦
11 hours ago
add a comment |
up vote
6
down vote
accepted
You need to use boolean arithmetic. Use the AND operator (&) to combine the incoming value AND the "mask" value (the value of the bits you do care about) and see if it equals the mask bit:
byte wanted = 0b11001110; // 207
byte incoming = 223; // for example 11011111
if ((wanted & incoming) == wanted) {
// whatever
}
The AND operator compares each bit of the bytes in turn. If they are BOTH 1 then the result is 1. Otherwise the result is 0. So the above gives:
wanted: 11001110
incoming: 11011111
AND: 11001110
And the result matches "wanted". If you had some other value for incoming it could look like this:
wanted: 11001110
incoming: 01011011
AND: 01001010
And you can see that the result doesn't match.
answered 15 hours ago
Majenko♦
65.8k42874
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
That is correct.
– Majenko♦
11 hours ago
add a comment |
up vote
6
down vote
accepted
up vote
6
down vote
accepted
You need to use boolean arithmetic. Use the AND operator (&) to combine the incoming value AND the "mask" value (the value of the bits you do care about) and see if it equals the mask bit:
byte wanted = 0b11001110; // 207
byte incoming = 223; // for example 11011111
if ((wanted & incoming) == wanted) {
// whatever
}
The AND operator compares each bit of the bytes in turn. If they are BOTH 1 then the result is 1. Otherwise the result is 0. So the above gives:
wanted: 11001110
incoming: 11011111
AND: 11001110
And the result matches "wanted". If you had some other value for incoming it could look like this:
wanted: 11001110
incoming: 01011011
AND: 01001010
And you can see that the result doesn't match.
answered 15 hours ago
Majenko♦
65.8k42874
You need to use boolean arithmetic. Use the AND operator (&) to combine the incoming value AND the "mask" value (the value of the bits you do care about) and see if it equals the mask bit:
byte wanted = 0b11001110; // 207
byte incoming = 223; // for example 11011111
if ((wanted & incoming) == wanted) {
// whatever
}
The AND operator compares each bit of the bytes in turn. If they are BOTH 1 then the result is 1. Otherwise the result is 0. So the above gives:
wanted: 11001110
incoming: 11011111
AND: 11001110
And the result matches "wanted". If you had some other value for incoming it could look like this:
wanted: 11001110
incoming: 01011011
AND: 01001010
And you can see that the result doesn't match.
answered 15 hours ago
Majenko♦
65.8k42874
answered 15 hours ago
Majenko♦
65.8k42874
answered 15 hours ago
Majenko♦
65.8k42874
answered 15 hours ago
Majenko♦
65.8k42874
65.8k42874
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
That is correct.
– Majenko♦
11 hours ago
add a comment |
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
That is correct.
– Majenko♦
11 hours ago
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
AH! Okay, that makes sense - I would want my 'mask' value to have bits set to '1' I care about, and '0' I don't. This would effectively force the 'don't care' bits to 0.
– Coyttl
12 hours ago
1
1
That is correct.
– Majenko♦
11 hours ago
That is correct.
– Majenko♦
11 hours ago
add a comment |
up vote
2
down vote
There are ways to mask off the don't care bits.
Say your example, 0b11xx1111.
Then
incomingByte = Serial.read();
incomingByte = incomingByte || 0b00110000; // make 4, 5 high
if (incomingByte == 0b11111111){
// got all 1s, do something
}
else {
// some 0s received, do something else
}
edited 11 hours ago
Juraj
6,4102925
answered 13 hours ago
CrossRoads
9637
add a comment |
up vote
2
down vote
There are ways to mask off the don't care bits.
Say your example, 0b11xx1111.
Then
incomingByte = Serial.read();
incomingByte = incomingByte || 0b00110000; // make 4, 5 high
if (incomingByte == 0b11111111){
// got all 1s, do something
}
else {
// some 0s received, do something else
}
edited 11 hours ago
Juraj
6,4102925
answered 13 hours ago
CrossRoads
9637
add a comment |
up vote
2
down vote
up vote
2
down vote
There are ways to mask off the don't care bits.
Say your example, 0b11xx1111.
Then
incomingByte = Serial.read();
incomingByte = incomingByte || 0b00110000; // make 4, 5 high
if (incomingByte == 0b11111111){
// got all 1s, do something
}
else {
// some 0s received, do something else
}
edited 11 hours ago
Juraj
6,4102925
answered 13 hours ago
CrossRoads
9637
There are ways to mask off the don't care bits.
Say your example, 0b11xx1111.
Then
incomingByte = Serial.read();
incomingByte = incomingByte || 0b00110000; // make 4, 5 high
if (incomingByte == 0b11111111){
// got all 1s, do something
}
else {
// some 0s received, do something else
}
edited 11 hours ago
Juraj
6,4102925
answered 13 hours ago
CrossRoads
9637
edited 11 hours ago
Juraj
6,4102925
edited 11 hours ago
Juraj
6,4102925
edited 11 hours ago
Juraj
6,4102925
6,4102925
answered 13 hours ago
CrossRoads
9637
answered 13 hours ago
CrossRoads
9637
answered 13 hours ago
CrossRoads
9637
9637
add a comment |
add a comment |
Coyttl is a new contributor. Be nice, and check out our Code of Conduct.
Coyttl is a new contributor. Be nice, and check out our Code of Conduct.
Coyttl is a new contributor. Be nice, and check out our Code of Conduct.
Coyttl is a new contributor. Be nice, and check out our Code of Conduct.
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