154 SI-Ethernet User Guide
Issue: 3
Figure 7-4 Non-cyclic parameter access state machine
7.4.1 Setting the destination node IP address
When setting the destination node IP address parameters, each parameter contains two octets of
the IP address. i.e. the most significant two octets (www.xxx) of the IP address is written to the base
address + 1 parameter and the least significant two octets (yyy.zzz) of the IP address is written to
the base address + 2 parameter.
Because each octet is an unsigned byte and the parameter used to store the combined value is a
signed 16-bit parameter, the following sequence must be used:
Base address + 1 (www.xxx)
1. “www” – bit shift left 8 times, clear upper 16 bits and lower 8 bits
2. “xxx” – clear upper 24 bits
3. Bitwise OR the two values
4. Correct the result for negative value
Base address + 2 (yyy.zzz)
1. “yyy” – bit shift left 8 times, clear upper 16 bits and lower 8 bits
2. “zzz” – clear upper 24 bits
3. Bitwise OR the two values
4. Correct the result for negative value
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