MAX5965A/MAX5965B
High-Power, Quad, Monolithic, PSE Controllers
for Power over Ethernet
26 ______________________________________________________________________________________
Message Format for Reading
The MAX5965A/MAX5965B read using the MAX5965A/
MAX5965B’s internally stored command byte as an
address pointer, the same way the stored command
byte is used as an address pointer for a write. The point-
er autoincrements after reading each data byte using the
same rules as for a write. Thus, a read is initiated by first
configuring the MAX5965A/MAX5965B’s command byte
by performing a write (Figure 11). The master now reads
‘n’ consecutive bytes from the MAX5965A/MAX5965B,
with the first data byte read from the register addressed
by the initialized command byte (Figure 12). When per-
forming read-after-write verification, remember to reset
the command byte’s address because the stored control
byte address autoincrements after the write.
Operation with Multiple Masters
When the MAX5965A/MAX5965B operate on a 2-wire
interface with multiple masters, a master reading the
MAX5965A/MAX5965B should use repeated starts
between the write which sets the MAX5965A/
MAX5965B’s address pointer, and the read(s) that take
the data from the location(s). It is possible for master 2 to
take over the bus after master 1 has set up the
MAX5965A/MAX5965B’s address pointer but before mas-
ter 1 has read the data. If master 2 subsequently resets
the MAX5965A/MAX5965B’s address pointer then master
1’s read may be from an unexpected location.
Command Address Autoincrementing
Address autoincrementing allows the MAX5965A/
MAX5965B to be configured with fewer transmissions
by minimizing the number of times the command
address needs to be sent. The command address
stored in the MAX5965A/MAX5965B generally incre-
ments after each data byte is written or read (Table 5).
The MAX5965A/MAX5965B are designed to prevent
overwrites on unavailable register addresses and unin-
tentional wrap-around of addresses.
Figure 11. Control and Single Data Byte Received
(20 páginas)
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