DS2505

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SILICON LABEL DESCRIPTION

The DS2505 16-kbit Add–Only Memory identifies and stores relevant information about the product to

which it is associated. This lot or product specific information can be accessed with minimal interface,

for example a single port pin of a microcontroller. The DS2505 consists of a factory-lasered registration

number that includes a unique 48-bit serial number, an 8-bit CRC, and an 8-bit Family Code (0BH) plus

16 kbits of user-programmable EPROM. The power to program and read the DS2505 is derived entirely

only a single data lead and a ground return. The entire device can be programmed and then write-

protected if desired. Alternatively, the part may be programmed multiple times with new data being

appended to, but not overwriting, existing data with each subsequent programming of the device. Note:

Individual bits can be changed only from a logical 1 to a logical 0, never from a logical 0 to a logical 1.

A provision is also included for indicating that a certain page or pages of data are no longer valid and

have been replaced with new or updated data that is now residing at an alternate page address. This page

address redirection allows software to patch data and enhance the flexibility of the device as a standalone

database. The 48-bit serial number that is factory-lasered into each DS2505 provides a guaranteed-

unique identity which allows for absolute traceability. The TO-92 and TSOC packages provide a

compact enclosure that allows standard assembly equipment to handle the device easily for attachment to

printed circuit boards or wiring.

Typical applications include storage of calibration constants,

maintenance records, asset tracking, product revision status and access codes.

OVERVIEW

The block diagram in Figure 1 shows the relationships between the major control and memory sections of

the DS2505. The DS2505 has three main data components: 1) 64-bit lasered ROM, 2) 16384-bits

EPROM Data Memory, and 3) 704 bits EPROM Status Memory. The device derives its power for read

operations entirely from the 1-Wire communication line by storing energy on an internal capacitor during

periods of time when the signal line is high and continues to operate off of this “parasite” power source

during the low times of the 1-Wire line until it returns high to replenish the parasite (capacitor) supply.

During programming, 1-Wire communication occurs at normal voltage levels and then is pulsed

momentarily to the programming voltage to cause the selected EPROM bits to be programmed. The

1-Wire line must be able to provide 12 volts and 10 milliamperes to adequately program the EPROM

portions of the part. Whenever programming voltages are present on the 1-Wire line a special high

voltage detect circuit within the DS2505 generates an internal logic signal to indicate this condition. The

hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one

of the four ROM Function Commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM.

These commands operate on the 64-bit lasered ROM portion of each device and can singulate a specific

device if many are present on the 1-Wire line as well as indicate to the bus master how many and what

types of devices are present. The protocol required for these ROM Function Commands is described in

Figure 8. After a ROM Function Command is successfully executed, the memory functions that operate

on the EPROM portions of the DS2505 become accessible and the bus master may issue any one of the

five Memory Function Commands specific to the DS2505 to read or program the various data fields. The

protocol for these Memory Function Commands is described in Figure 5. All data is read and written

least significant bit first.

64-BIT LASERED ROM

Each DS2505 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.

The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (See Figure 3.)

The 64-bit ROM and ROM Function Control section allow the DS2505 to operate as a 1-Wire device and

follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The memory functions required

to read and program the EPROM sections of the DS2505 are not accessible until the ROM function