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

The SX48 has two 16 bit hardware timers that are mostly unrelated to the RTCC 8 bit timer.  It is hard to get a clear picture from the published documents without some digging.

They are intended mainly to do other things, like generate PWM for motor control in parallel with the main program running other tasks. Generally, the ISR routine is independent of the timer routines, though I can imagine more creative and exotic programing with the timers sharing the ISRs interrupt.  I don't know if it would be good or useful.   If one does enable the two additional timers, then it is possible to enable an internal interupt or use a pin to provide an external interput.  

I've looked at the interrupt possiblities and really wondered about all the choices.  I suspect that if you want to use the WTD with postscaller, it may block using the RTCC for ISRs.  If that is true, it appears that you can use one of the 16bit timers to take over the RTCCs functions.  This is all speculation at this point.

NONE of this applies to SX28 as it doesn't have the extra two timers.

I suppose that you want to know is the DEFAULT behavior is that the two additional timers are not in play. IN SXAsm, the timers are selected by choosing the proper MODE register to reach two Timer Control Registers A & B for each timer and then toggling the right enable bits.  Each of the Timers is associated with a port, Port B and Port C for inputs or outputs and control.  I am not really clear on how SX/B handles all that.  I suspect it is all does pretty close to the way the SXasm handles it unless someone has written specialized uses, like PWM or Capture and Compare. 

Take a look at the diagram in the SX48/52 PDF for the interupt logic on page 23.  The main - page one -block diagram seems wrong as it doesn't show an internal interupt connection between the two additional timers and the interupts that use the interupt stack.  If you are going to work with these additional timers, you may need to read and fully understand that PDF anyway.

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