Rainbow-electronics MAX6948B Manual do Utilizador descarregar pdf (Página 24)

High-Efficiency PWM LED Driver with Boost

Converter and Five Constant-Current GPIO Ports

MAX6948B

Figure 13. Command Byte Received

Figure 14. Command and Single Data Byte Received

Figure 15. N Data Bytes Received

Message Format for Writing the LED Driver

A write to the MAX6948B comprises the transmission of

the slave address with the R/W bit set to zero, followed

by at least 1 byte of information. The first byte of infor-

mation is the command byte. The command byte deter-

mines which register of the MAX6948B is to be written by

the next byte, if received. If a STOP condition is detected

after the command byte is received, the MAX6948B

takes no further action (Figure 13) beyond storing the

command byte.

Any bytes received after the command byte are data

bytes. The first data byte goes into the internal regis-

ter of the MAX6948B selected by the command byte

(Figure 14).

If multiple data bytes are transmitted before a STOP

condition is detected, these bytes are generally stored

in subsequent MAX6948B internal registers because

the command-byte address generally autoincrements

(Table 1).

Message Format for Reading

The MAX6948B is read using the MAX6948B’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 pointer generally autoincrements

after each data byte is read using the same rules as for

a write (Table 1). Thus, a read is initiated by first config-

uring the MAX6948B’s command byte by performing a

write (Figure 13). The master can now read n consecu-

tive bytes from the MAX6948B, with the first data byte

being read from the register addressed by the initialized

command byte. When performing read-after-write verifi-

cation, remember to reset the command byte’s address

because the stored command-byte address is generally

autoincremented after the write (Figure 15, Table 1).

S A A

0SLAVE ADDRESS

COMMAND BYTE

ACKNOWLEDGE FROM MAX6948B

D15 D14 D13 D12 D11 D10 D9 D8

COMMAND BYTE IS STORED ON RECEIPT OF

STOP CONDITION

ACKNOWLEDGE FROM MAX6948B

R/W

S A A A P0SLAVE ADDRESS COMMAND BYTE DATA BYTE

BYTE

AUTOINCREMENT MEMORY ADDRESS

D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6

ACKNOWLEDGE FROM MAX6948B ACKNOWLEDGE FROM MAX6948B

ACKNOWLEDGE FROM MAX6948B

HOW COMMAND BYTE AND DATA BYTE MAP INTO

MAX6948B REGISTERS

R/W

S A A A P0SLAVE ADDRESS COMMAND BYTE DATA BYTE

BYTES

D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6

ACKNOWLEDGE FROM MAX6948B ACKNOWLEDGE FROM MAX6948B

ACKNOWLEDGE FROM MAX6948B

HOW COMMAND BYTE AND DATA BYTE MAP INTO

MAX6948B REGISTERS

R/W

AUTOINCREMENT MEMORY ADDRESS

1 2 ... 19 20 21 22 23 24 25 26 27 28

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