In SX Microcontrollers, SX/B Compiler and SX-Key Tool, JonnyMac wrote:

Bill,

Masking is a pretty common in programming, especially embedded programming.  I'm working on a book called "Practical SX/B" right now and make sure that the topic gets good coverage.  What's important to understand how the basic operators | (or), & (and) and ~ (not) behave.  With & (and), anything "anded" with zero is zero, so you can clear bits by putting zeros into the positions you want cleared, hence:

[code]someValue = someValue & $0F[/code]

will cause the the upper bits of 'someValue' to be cleared, while the lower bits will remain intact (1 stays 1, 0 stays 0).  Using masking and SWAP generates less assembly code in SX/B that shifting by four bits.

Since I wrote StampWorks (yes, I am the artist formerly known as Jon Williams) I think it's a great book, but it is focused on the BS2 and a lot of very cool tricks that are built into the BASIC Stamp that don't exist in other languages, even SX/B.  My new book points out those differences when appropriate to help BS2 programmers make the move to SX/B without stress or pain.

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