DS1972: 1024-Bit EEPROM iButton

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The protection control registers determine how incoming data on a Write Scratchpad command is loaded into the

scratchpad. A protection setting of 55h (Write Protect) causes the incoming data to be ingnored and the target

address main memory data to be loaded into the scratchpad. A protection setting of AAh (EPROM mode) causes

the logical AND of incoming data and target address main memory data to be loaded into the scratchpad. Any

other protection control register setting leaves the associated memory page open for unrestricted write access.

Protection control byte settings of 55h or AAh also write protects the protection control byte. The protection-control

byte setting of 55h does not block the copy. This allows write-protected data to be refreshed (i. e., reprogrammed

with the current data) in the device.

The copy protection byte is used for a higher level of security, and should only be used after all other protection

control bytes, user bytes, and write-protected pages are set to their final value. If the copy protection byte is set to

55h or AAh, all copy attempts to the register row and user byte row are blocked. In addition, all copy attempts to

write-protected main memory pages (i. e., refresh) are blocked.

ADDRESS REGISTERS AND TRANSFER STATUS

The DS1972 employs three address registers: TA1, TA2, and E/S (Figure 6). These registers are common to many

other 1-Wire devices but operate slightly differently with the DS1972. Registers TA1 and TA2 must be loaded with

the target address to which the data is written or from which data is read. Register E/S is a read-only transfer-

status register, used to verify data integrity with write commands. E/S bits E2:E0 are loaded with the incoming

T2:T0 on a Write Scratchpad command, and increment on each subsequent data byte. This is in effect a byte-

ending offset counter within the 8-byte scratchpad. Bit 5 of the E/S register, called PF, is a logic 1 if the data in the

scratchpad is not valid due to a loss of power or if the master sends less bytes than needed to reach the end of the

scratchpad. For a valid write to the scratchpad, T2:T0 must be 0 and the master must have sent 8 data bytes. Bits

3, 4, and 6 have no function; they always read 0. The highest valued bit of the E/S register, called AA or

Authorization Accepted, acts as a flag to indicate that the data stored in the scratchpad has already been copied to

the target memory address. Writing data to the scratchpad clears this flag.

Figure 6. Address Registers

Bit #

7

6

5

4

3

2

1

0

Target Address (TA1)

T7

T6

T5

T4

T3

T2

T1

T0

Target Address (TA2)

T15

T14

T13

T12

T11

T10

T9

T8

Ending Address with

Data Status (E/S)

(Read Only)

AA

0

PF

0

0

E2

E1

E0