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

Please let me bail in here...

There are three options for the IRC_CAL SASM directive:

IRC_SLOW
IRC_4MHZ
IRC_FAST

When your code contains any OSC directive other than OSCxMHZ to activate the internal RC clock generator, either include the

IRC_CAL IRC_SLOW, or IRC_CAL IRC_FAST directive to avoid that the SX-Key IDE (unnececessarily) detemines the SX-internal RC clock speed. As the SX-Key IDE does not perform the speed-adjustment in this case, chip programming will be faster. As you are going to use an external clock-generating component anyway, there is no need to calibrate the SX-internal RC clock in such cases.

In case you are going to use the internal RC oscillator, i.e. when your code contains a DEVICE OSCxMHZ directive, add an

IRC_CAL IRC_4MHZ

directive if you want to let the SX-Key IDE trim the internal RC clock as close as possible to 4 MHz. When the precision of the internal RC clock is not an issue for your application, you may either include the IRC_SLOW, or IRC_FAST directive instead. Again, the SX-Key will not perform an internal RC calibration in this case, so the device-programming process will be a bit faster.

Finally: The internal RC clock (and an external RC clock either) are not very precise at all. Even with an IRC_CAL IRC_4MHZ, the internal RC oscillator may not be stable enough over a longer time period to control time-critical operations, like serial transmitters/receivers, timers, etc.

Therefore, make your SX happy, and add an external clock device, like a resonator, and xtal, or a solid-state clock device. See the SX data sheets for more details.

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