Difference between revisions of "Setting Clearing and Copying bits of data"
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[[Category:6502]] | [[Category:6502]] | ||
| + | ===Clearing bits=== | ||
AND xx will clear the bits in A that are also clear in xx, for example: | AND xx will clear the bits in A that are also clear in xx, for example: | ||
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%abcdefgh %01010101 %0b0d0f0h | %abcdefgh %01010101 %0b0d0f0h | ||
| + | ===Setting bits=== | ||
ORA xx will set the bits in A that are also set in xx, for example: | ORA xx will set the bits in A that are also set in xx, for example: | ||
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%abcdefgh %01010101 %a1c1e1g1 | %abcdefgh %01010101 %a1c1e1g1 | ||
| + | ===Toggling bits=== | ||
EOR xx will toggle the bits in A that are set in xx, for example: | EOR xx will toggle the bits in A that are set in xx, for example: | ||
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%abcdefgh %01010101 %aBcDeFgH | %abcdefgh %01010101 %aBcDeFgH | ||
| − | To clear the bits in A that are ''set'' in xx, use both ORA and EOR, for example: | + | ===Clear complementary bits=== |
| − | + | To clear the bits in A that are ''set'' in xx, use both ORA and EOR, for | |
| + | example: | ||
A xx after ORA xx after EOR xx | A xx after ORA xx after EOR xx | ||
%abcdefgh %01010101 %a1c1e1g1 %a0c0e0g0 | %abcdefgh %01010101 %a1c1e1g1 %a0c0e0g0 | ||
| − | You can copy a number of bits to a memory location without changing the other bits using EOR and AND. For example, to copy the top four bits of A into a memory location without changing the bottom four bits, use the following: | + | ===Copying bits=== |
| + | You can copy a number of bits to a memory location without changing the | ||
| + | other bits using EOR and AND. For example, to copy the top four bits of A | ||
| + | into a memory location without changing the bottom four bits, use the | ||
| + | following: | ||
A=12345678 dst=abcdefgh | A=12345678 dst=abcdefgh | ||
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PLA | PLA | ||
AND #&F0:ORA dst:STA dst | AND #&F0:ORA dst:STA dst | ||
| + | |||
| + | ===Swapping data=== | ||
| + | Data can be swapped between two different memory locations without using a | ||
| + | temporary location by EORing the data in both directions: | ||
| + | |||
| + | LDA val1:EOR val2:STA val1 | ||
| + | EOR val2:STA val2 | ||
| + | EOR val1:STA val1 | ||
| + | |||
| + | This is in contrast to using a temporary location or register such as with: | ||
| + | |||
| + | LDA val1:STA tmp | ||
| + | LDA val2:STA val1 | ||
| + | LDA tmp:STA val2 | ||
[[User:Jgharston|Jgharston]] 18:58, 30 August 2007 (BST) | [[User:Jgharston|Jgharston]] 18:58, 30 August 2007 (BST) | ||
| + | [[User:Jgharston|Jgharston]] ([[User talk:Jgharston|talk]]) 07:10, 30 June 2018 (CEST) | ||
Latest revision as of 06:10, 30 June 2018
Contents
Clearing bits
AND xx will clear the bits in A that are also clear in xx, for example:
A xx after AND xx %abcdefgh %01010101 %0b0d0f0h
Setting bits
ORA xx will set the bits in A that are also set in xx, for example:
A xx after ORA xx %abcdefgh %01010101 %a1c1e1g1
Toggling bits
EOR xx will toggle the bits in A that are set in xx, for example:
A xx after EOR xx %abcdefgh %01010101 %aBcDeFgH
Clear complementary bits
To clear the bits in A that are set in xx, use both ORA and EOR, for example:
A xx after ORA xx after EOR xx %abcdefgh %01010101 %a1c1e1g1 %a0c0e0g0
Copying bits
You can copy a number of bits to a memory location without changing the other bits using EOR and AND. For example, to copy the top four bits of A into a memory location without changing the bottom four bits, use the following:
A=12345678 dst=abcdefgh EOR dst ******** abcdefgh AND #&F0 ****0000 abcdefgh EOR dst 1234efgh abcdefgh STA dst 1234efgh 1234efgh
This is much more efficient than the usual code:
PHA LDA dst:AND #&0F:STA dst PLA AND #&F0:ORA dst:STA dst
Swapping data
Data can be swapped between two different memory locations without using a temporary location by EORing the data in both directions:
LDA val1:EOR val2:STA val1
EOR val2:STA val2
EOR val1:STA val1
This is in contrast to using a temporary location or register such as with:
LDA val1:STA tmp LDA val2:STA val1 LDA tmp:STA val2
Jgharston 18:58, 30 August 2007 (BST) Jgharston (talk) 07:10, 30 June 2018 (CEST)
