Sundance Spas ST201 - Manual (Page 43)

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Sundance Technology ST201 PRELIMINARY draft 2
I/O REGISTERS
The host interacts with the ST201 mainly through slave registers, which occupy 128 bytes in the host sys-
tem’s I/O space, memory space, or both. Generally, registers are referred to as “I/O registers”, implying
that the registers may in fact be mapped and accessed by the host system in memory space. I/O registers
must be accessed with instructions that are no larger than the bit-width of that register. For instance, even
though the FramesWithExcessiveDeferral, FramesLostRxErrors, and FramesWithDeferredXmission regis-
ters all appear in the same double word at offset 78, it is not legal to read all three registers with a single
32-bit I/O read instruction.
The ST201 I/0 register layout is show in Figure 11.