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read/write operations


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Good afternoon,

Read-modify-write means that the port is read, the bit selected is set or cleared, and the result is written to the port. The disadvantage of this is that the output that is driven high by the output may be overloaded and read as low (or vice-versa) as the output latch is not read only the actual pin. This is why sometimes it is good to use 'shadow' registers to modify, then transfer their contents to the port.

Tri-state means that the output driver is disabled- writing a 0 or 1 to the latch will not affect the external circuitry.

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