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

Let me place a general comment about SX interrupts here:

No matter, how many interrupt sources are available in the "small" and "large" SXes - there is always only one interrupt level, i.e. whatever source fires an interrupt, program execution will always branch to address $000 in page 0. So, the SX does not have any "vectored" interrupts as can be found in other controllers where different sources of interrupts cause the program execution branch to different locations in program memory.

This makes is a bit more tricky to handle multiple interrupt sources in one application with the SX, as the ISR code needs to figure out the interrupt source at the very beginning, and then branch to the associated interrupt handlers.

Furthermore, the SX can only handle one interrupt level, i.e. as soon as one interrupt has been fired, no matter from what source, further interrupts are disabled until a RETI or RETIW instruction is executed. So, when another event occurs that should trigger an interrupt while the ISR code is executed, this one might be missed, or its detection will be delayed until the execution returns from handling the recent interrupt.

Although it is possible to handle multiple interrupt sources with the SX within one application, I suggest that you begin with handling just one of the possible interrupt sources when you are new to this topic.

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