Serial Communications Module

For Evaluation Kits

_____________________________________________________________________

7

Example: Sending the byte sequence {0x82, 0x20,

0x45, 0x67, 0x89} to DS3900 causes it to:

1.

Send a 2-wire Start condition.

2.

using Set Packet Device Address).

3.

Write the memory address (0x20).

4.

Write data 0x45 (to address 0x20).

5.

Write data 0x67 (to address 0x21).

6.

Write data 0x89 (to address 0x22).

7.

Send a 2-wire Stop condition.

8.

If the 2-wire device acknowledges all bytes of the

data transmission, the DS3900 will return (0x82);

otherwise it will return an error code (0xFA).

The Packet Read command allows up to 16 data bytes

to be read with a single 2-byte instruction. The read

operation will be sent to the device operating at the

device address set using the Set Packet Device

Address command. The first byte sent for a Packet

Read command is 0x9%, where % is one less than the

number of bytes to read (e.g. 0x95 reads 6 bytes). The

second byte sent determines the memory address to

begin reading from within the device that is being

addressed. After the second byte is received, the

DS3900 will begin a dummy write cycle that will

address the part as if writing, and write out the device

address followed by the memory address. Then a

restart condition is generated, and the device's read

address is sent to start the read operation. The DS3900

will begin reading the data from the 2-wire part and

sending it back to the PC. The DS3900 will acknowl-

edge all but the last data byte sent from the 2-wire part.

The last byte is Not Acknowledged, which is a standard

2-wire practice. Once it has read %+1 data bytes and

sent them to the PC, the DS3900 will send 0x9% if the

read occurred without error, or 0xFA if a problem did

occur.

Example: Sending the byte sequence {0x91, 0x20} to

the DS3900 will cause it to:

1.

Send a 2-wire Start command.

2.

Write the device address R/W =0 (set previously

using Set Packet Device Address).

3.

Write the memory address 0x20.

4.

Send a 2-wire Start command (repeated-start).

5.

Write the device address R/W =1 (set previously

using Set Packet Device Address).

6.

Read the data (at address 0x20), send 2-wire

Acknowledge on 9th clock cycle, and send the

data read back to the PC.

7.

Read the data (at address 0x21), send 2-wire Not

Acknowledge on 9th clock cycle, and send the

data read back to the PC.

SEND START COMMAND, WRITE 0x23 TO POT 0, AND 0X34 TO POT 1, SEND STOP COMMAND

SEQ #

1ST BYTE SENT

2ND BYTE SENT

1ST BYTE RETURNED

2ND BYTE RETURNED

DESCRIPTION

1

0xA0

0x00

Place holder

0xB0

Command ack

None

2-wire start

2

0xA1

0x50

Data

0xB1

Command ack

None

Send 0x50 over

2-wire bus

(send write DS1803 addr)

3

0xA1

0xA9

Data

0xB1

Command ack

None

Send 0xA9 over

2-wire bus

(write pot 0 command)

4

0xA1

0x23

Data

0xB1

Command ack

None

Send 0x23 over

2-wire bus

(write 0x23 to pot 0)

5

0xA1

0x34

Data

0xB1

Command ack

None

Send 0x34 over

2-wire bus

(write 0x23 to pot 1)

6

0xA3

0x00

Place holder

0xB3

Command ack

None

2-wire stop

Table 4. Example of Writing to a DS1803