Rainbow Electronics MAX5971B User Manual

Page 25

______________________________________________________________________________________ 25

MAX5971B

Single-Port, 40W, IEEE 802.3af/at,

PSE Controller with I

Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register
of the MAX5971B selected by the command byte (Figure
12). The control byte address then autoincrements, if
possible (see Table 6), and then waits for the next data
byte or a STOP condition.
If multiple data bytes are transmitted before a STOP con-
dition is detected, these bytes are stored in subsequent
MAX5971B internal registers as the control byte address
autoincrements (Figure 13). If the control byte address
can no longer increment, any subsequent data sent con-
tinues to write to that address.

Message Format for Reading

A read command for the MAX5971B comprises the
device slave address transmission with the R/W bit set
to 1, followed by at least one byte of information. As
with a write command, the first byte of information is the
command byte. The MAX5971B then reads using the
internally stored command byte as an address pointer,
the same way the stored command byte is used as an
address pointer for a write. This pointer autoincrements
after reading each data byte using the same rules as for
a write, though the master now sends the acknowledge
bit after each read receipt (Figure 14). When performing
read-after-write verification, remember to reset the com-
mand byte’s address because the stored control byte
address autoincrements after the write.

Figure 12. Write Format: Control and Single Data Byte Written

Figure 13. Write Format: Control and n Data Bytes Written

Figure 14. Read Format: Control and n Data Bytes Read

R/W

CB7

ACK

CB6 CB5 CB4 CB3 CB2 CB1 CB0

CONTROL BYTE STORED ON STOP CONDITION

ACKNOWLEDGE FROM THE MAX5971B

SLAVE ADDRESS

CONTROL BYTE

DATA BYTE (1 BYTE)

WORD ADDRESS AUTOINCREMENT

ACKNOWLEDGE FROM THE MAX5971B

ACK

SLAVE ADDRESS

CONTROL BYTE

DATA BYTE (n BYTES)

CB7 CB6 CB5 CB4 CB3 CB2 CB1 CB0

CONTROL BYTE STORED ON STOP CONDITION

ACKNOWLEDGE FROM THE MAX5971B

R/W

WORD ADDRESS AUTOINCREMENT

REPEAT FOR n BYTES

ACKNOWLEDGE FROM THE MAX5971B

ACK

SLAVE ADDRESS

CONTROL BYTE

DATA BYTE (n BYTES)

CB7 CB6 CB5 CB4 CB3 CB2 CB1 CB0

CONTROL BYTE STORED ON STOP CONDITION

ACKNOWLEDGE FROM THE MAX5971B

R/W

ACKNOWLEDGE FROM THE MASTER

ACKNOWLEDGE FROM THE MAX5971B

WORD ADDRESS AUTOINCREMENT

REPEAT FOR n BYTES