High-Power, Quad, PSE Controller
for Power-Over-Ethernet
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Message Format for Reading
The MAX5952 reads using the MAX5952s 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 pointer auto-increments after
reading each data byte using the same rules as for a
write. Thus, a read is initiated by first configuring the
MAX5952s command byte by performing a write (Figure
11). The master now reads n consecutive bytes from
the MAX5952, with the first data byte read from the regis-
ter addressed by the initialized command byte (Figure
12). When performing read-after-write verification,
remember to reset the command bytes address
because the stored control byte address auto-incre-
ments after the write.
Operation with Multiple Masters
When the MAX5952 operates on a 2-wire interface with
multiple masters, a master reading the MAX5952
should use repeated starts between the write which
sets the MAX5952s 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 MAX5952s address pointer but before master 1
has read the data. If master 2 subsequently resets the
MAX5952s address pointer then master 1s read may
be from an unexpected location.
Command Address Auto-Incrementing
Address auto-incrementing allows the MAX5952 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 MAX5952
generally increments after each data byte is written or
read (Table 5). The MAX5952 is designed to prevent
overwrites on unavailable register addresses and unin-
tentional wrap-around of addresses.
Figure 11. Control and Single Data Byte Received
S
A
A
A
P
0
SLAVE ADDRESS
CONTROL BYTE
DATA BYTE
ACKNOWLEDGE FROM MAX5952
1 BYTE
AUTO-INCREMENT
MEMORY WORD ADDRESS
D15  D14  D13  D12  D11  D10   D9   D8
D1   D0
D3   D2
D5   D4
D7   D6
HOW CONTROL BYTE AND DATA BYTE MAP
INTO THE REGISTER
ACKNOWLEDGE FROM MAX5952
ACKNOWLEDGE FROM MAX5952
R/W
Figure 12. n Data Bytes Received
S
A
A
A
P
0
SLAVE ADDRESS
CONTROL BYTE
DATA BYTE
ACKNOWLEDGE FROM MAX5952
n BYTES
AUTO-INCREMENT
MEMORY WORD ADDRESS
D15  D14  D13  D12  D11  D10   D9   D8
D1   D0
D3   D2
D5   D4
D7   D6
HOW CONTROL BYTE AND DATA BYTE MAP
INTO THE REGISTER
ACKNOWLEDGE FROM MAX5952
ACKNOWLEDGE FROM MAX5952
R/W
Table 5. Auto-Increment Rules
COMMAND BYTE
ADDRESS RANGE
AUTO-INCREMENT BEHAVIOR
0x00 to 0x26
Command address auto-increments
after byte read or written
0x26
Command address remains at 0x26
after byte written or read