TMP141

SBAS347 − MARCH 2005

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9

Read and Write Transactions

A complete Read transmission consists of a Start Bit, the device number, the Register Number, R/W = 1, the data bits, an

even parity bit, and an Acknowledge bit. The most significant bit is sent first.

Read Transaction

START

DEVICE NUMBER

REGISTER NUMBER

R/W

8 or 16 DATA BITS

EP

ACK

M

M

M

M

M

M

M

M

M

M

M

S

… S

S

M

A complete Write transmission consists of a Start Bit, the device number, the Register Number, R/W = 0, the data bits, an

even parity bit, and an Acknowledge bit.

Write Transaction

START

DEVICE NUMBER

REGISTER NUMBER

R/W

8 or 16 DATA BITS

EP

ACK

M

M

M

M

M

M

M

M

M

M

M

M

… M

M

S

M indicates that the bit is initiated and controlled by the master. S indicates that the bit is initiated by the master but controlled

by the slave; if the data is a ‘1’, the slave lengthens the time that the bus is held low to signal a ‘1’.

The device number is three bits long. Device number 0 is reserved for a broadcast to all devices, leaving address space

for seven slaves.

The Register Number is six bits long.

The R/W is a ‘1’ for a read operation. The R/W bit is a ‘0’ for a write operation.

In a Write operation, the data bits and parity are sent by the master. In a Read operation, the data bits and parity are sent

by the TMP141. Data length is eight bits for registers 0, 4, and 20h. All other registers are 16 bits long. The number of bits

transmitted or received depends on the length of the register: 8 bits for an 8-bit register and 16 bits for a 16-bit register.

Even parity (EP) is used on the SensorPath. The parity calculation includes all bits after the Start Bit, up to and including

the parity bit. Thus, the parity calculation includes the device number, the Register Number, R/W, the data bits, and the

parity bit. In a Write operation, the TMP141 checks the parity sent by the master before generating the Acknowledge bit.

The Acknowledge bit is sent by the receiving unit. In a Write operation, the Acknowledge bit will come from the TMP141.

In a Read operation, the master generates the Acknowledge bit.

ACKNOWLEDGE Bit Definition:

1: A complete data transmission was completed without a parity error.

0: An error was detected. (BER in the Status Register will be set. An Attention Request will be generated.)