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

ichidan, James,

according to the SX20/28 and the SX48/52 datasheets, the IREAD instruction takes four cycles in turbo mode, and not just one. Interstingly, the Ubicom SX20/28 datasheet states that one cycle is taken in compatibility mode, and four in turbo mode. If you look at other instructions, like CALL, it states 2 for compatible and 3 for turbo mode, or for a MOV instruction, it states 1 for both modes. The explanation for this can be found in the dataseheet as well:

"The instruction execution time is derived by dividing the
oscillator frequency by either one (Turbo mode) or four
(Compatible mode). The divide-by factor is selected
through the FUSE Word register."

Nevertheless, this is a bit confusing, and should be corrected in a new version of the datasheet.

Back to IREAD, I assume that four cycles are correct in turbo mode as the complete instruction pipeline will be dicarded - so I'm going to fix that in SXSim.

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