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

1. This is a trick I learned from PJV, one of the aforementioned gurus.  Here's the deal: the interrupt runs at a known rate so we can use that rate for external timing.  This is important because time-based functions like PAUSE get hosed up when we use interrupts.  This is why -- as in this program -- when we're using an interrupt the code inside DELAY_MS changes; in this case it simply counts interrupt cycles which are marked by setting the isrFlag to 1.  In your program the interrupt rate is conveniently set to 1 millisecond so DELAY_MS is very straightforward: it clears the flag, waits for another, and then decrements the delay (millisecond) counter until it reaches zero.  

In the end, setting isrFlag to 1 is way to tell the foreground the the ISR has run.

2. There are two ways to insert Assembly statements into an SX/B program: the \ character allows for a single line, or we can put in a block of statements using ASM..ENDASM.  For one or two lines I tend to use \, for more than that I usually have an ASM..ENDASM block.

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