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AMC6821

SBAS386C – MAY 2006 – REVISED JULY 2007

Table 6. Write Multiple Bytes

S

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

DATA

ACK

DATA

ACK

7-bit AMC6821 slave

8-bit register address of

First 8-bit data written

Second 8-bit data written

address

first register to be written

first register

second register

DATA

ACK

...

DATA

ACK

P

Third 8-bit data written third register

Last 8-bit data

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).

The first register is the one to which the first data byte is written. The next register is the second register. If the

bus master continues to transfer data into the AMC6821 after writing the last location, all data are ignored until

the operation stops.

Table 7. Read Byte

S

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

Sr

SLAVE ADDRESS

RD

ACK

DATA

NACK

P

7-bit AMC6821 slave

7-bit AMC6821 slave

8-bit data from

8-bit register address

address

address

register

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0); RD = read (bit

value of 1);

NACK = not acknowledged; Sr = repeated start condition.

Table 8. Read Multiple Bytes

S

SLAVE ADDRESS

WR

ACK

COMMAND

ACK

Sr

SLAVE ADDRESS

RD

ACK

DATA

ACK

7-bit AMC6821 slave

Address of first

7-bit AMC6821 slave

8-bit data from first

address

register to be read

address

register

DATA

ACK

...

DATA

NACK

P

8-bit data from second register

Last 8-bit data

S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0); RD = read (bit

value of 1);

NACK = not acknowledged; Sr = repeated start condition.

The first register is the one from which the first data byte is transmitted. The next register is the second register.

If the bus master continues clocking data out after reading the last location (0x3F), the value 0x00 is sent out

until the operation stops.

The AMC6821 is entirely controlled by the registers. All registers are 8-bit. The AMC6821 has an address pointer

register; the value of the address pointer register determines the register to be written to or read from. To write

data to the device register or read data from it, the address pointer register must be set properly. Data can then

be written into or read from that register. The command issued by the bus master always contains the initial

value of the address pointer register. The command is constructed as shown in Table 9.

Bit 7 (MSB)

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0 (LSB)

0

0

ADDR5

ADDR4

ADDR3

ADDR2

ADDR1

ADDR0

(1)

ADDR[5:0] is the address of the register that is accessed first. The register address is stored in the address pointer register.

In the send byte operation, the bus master writes the address of a specified device register into the address

pointer register.

In the receive byte operation, the bus master reads the data back from the device register addressed by the

address point register.

In the write byte operation, the bus master sets the address pointer register to the address of a specified device

register, then writes 8-bit data into it. In the read byte operation, the SMBus master sets the address pointer

register to the address of a specified device register first, then reads 8-bit data back from it.

Copyright © 2006–2007, Texas Instruments Incorporated

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