Rainbow Electronics MAX5945 User Manual

Page 21

Message Format for Writing the MAX5945

A write to the MAX5945 comprises of the MAX5945’s
slave address transmission with the R/W bit set to 0, fol-
lowed by at least one byte of information. The first byte
of information is the command byte (Figure 11). The
command byte determines which register of the
MAX5945 is written to by the next byte, if received. If
the MAX5945 detects a STOP condition after receiving
the command byte, then the MAX5945 takes no further
action beyond storing the command byte. Any bytes
received after the command byte are data bytes. The
first data byte goes into the internal register of the

MAX5945 selected by the command byte. If the
MAX5945 transmits multiple data bytes before the
MAX5945 detects a STOP condition, these bytes store
in subsequent MAX5945 internal registers because the
control byte address auto-increments.

Any bytes received after the control byte are data
bytes. The first data byte goes into the internal register
of the MAX5945 selected by the control byte (Figure 8).

If multiple data bytes are transmitted before a STOP
condition is detected, these bytes are stored in subse-
quent MAX5945 internal registers because the control
byte address auto-increments.

MAX5945

Quad Network Power Controller

for Power-Over-LAN

______________________________________________________________________________________

Figure 11. Control Byte Received

SLAVE ADDRESS

CONTROL BYTE

ACKNOWLEDGE FROM MAX5945

D15

D14

D13

D12

D11

D10

CONTROL BYTE IS STORED ON RECEIPT OF STOP CONDITION

R/W

Figure 12. Control and Single Data Byte Received

SLAVE ADDRESS

CONTROL BYTE

DATA BYTE

ACKNOWLEDGE FROM MAX5945

1 BYTE

AUTO-INCREMENT

MEMORY WORD ADDRESS

D15 D14 D13 D12 D11 D10

HOW CONTROL BYTE AND DATA BYTE MAP

INTO THE REGISTER

ACKNOWLEDGE FROM MAX5945

R/W

Figure 13. ‘n’ Data Bytes Received

SLAVE ADDRESS

CONTROL BYTE

DATA BYTE

ACKNOWLEDGE FROM MAX5945

n BYTES

AUTO-INCREMENT

MEMORY WORD ADDRESS

D15 D14 D13 D12 D11 D10

HOW CONTROL BYTE AND DATA BYTE MAP

INTO THE REGISTER

ACKNOWLEDGE FROM MAX5945

R/W