DS1205S datasheet(2/17 Pages) DALLAS

2 / 17 page

DS1205S

021798 2/17

INTERFACES

Two interfaces to the DS1205S are provided.

The

1-wire interface requires a 1-wire I/O command for ad-

dressing the device. An additional function command

word is then passed through the 1-wire interface to ac-

cess the various DS1205S functions. The 3-wire inter-

face (data (DQ), reset (RST), and clock (CLK)) requires

only the function command word. The four 1-wire I/O

commands that deal with the unique lasered ROM are

available only through the 1-wire interface. All other

functions are available through either interface.

FUNCTIONS

A command word written written to the DS1205S Multi-

Key specifies the operation to be performed and the

partition to be operated on. There are two classes of

functions available. One class includes operations on

the read/write secure partitions. The other class in-

cludes operations on the read/write scratchpad

(Figure 1).

COMMAND OPERATIONS Figure 1

COMMAND WORD

SUBKEY 0

SUBKEY 1

SUBKEY 2

SECURE READ/WRITE

SCRATCHPAD

(24 BITS)

READ/WRITE

The 24 bit function command word is organized into

three fields of eight bits each. These one byte fields in-

clude the function to be performed, the memory partition

to be accessed and the starting byte address for the

data transfer operation. The starting byte address and

the partition codes are required to be given in both real

and complement form. If these values do not match, ac-

cess to the part will be denied (Figure 2).

The function command word is presented to the

DS1205S LSB first. The first byte contains the 8-bit

function code that defines which of the six valid function

codes is to be executed. Each function code is valid for

only certain partition and starting address combina-

tions. Figure 3 illustrates the valid partition code, start-

ing address and function code combinations. The se-

cond byte consists of the 2-bit partition code, identifying

which partition is being accessed, and the 6-bit starting

byte address, which specifies where to start the access

of the given partition. The third byte consists of the com-

plement of the 2-bit partition code and the complement

of the 6-bit starting byte address.

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