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

If you're going to do ISR-based serial I think it best to use assembly and switch banks manually; the code is very trim and will consume less time in the ISR.  SX/B wants to point to bank 0 for normal variables so by putting your serial variables into an array (which forces them into something beyond bank 0) you end up preserving your "normal" variable space.  I lifted the serial routines from Al Williams' book and use them all the time in my SX/B programs when I need background serial.  I've attached my UART VP work file that you can experiment with.  Just set your ISR to 1/4 the fastest bit time you expect.  The program that's attached has bit settings for 2400 to 57.6K baud.

Note, too, that flags and tix variables are assigned first -- there's a reason for this: If you look at the list file you'll see that the first three bytes of an SX28 program will make it into the global space ($00-$0F) so this means these variables can be accessed without concern of the current bank setting.

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