Hornet-Specific Registers

I/O     R/W
Address Mode    Description
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0022h   R/W     HIR - Hornet index register
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0023h   R/W     HDR - Hornet data register
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0028h   R/W     CPU Power Control
                bits 7-3 undefined when read, must write 0
                bit  1 = 1 enter idle mode at next halt cycle
                bit  0 = 1 enter powerdown mode at next halt cycle
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0029h   R/W     bits 7-0 undefined when read, must write 0
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002Ch   R       bits 7-4 reserved
                bits 3-0 Stepping ID (0001 for first parts)
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002Dh   -       reserved
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