DS2505 Maxim, DS2505 Datasheet - Page 2

• Manufacturer Part Number: DS2505
• Manufacturer: Maxim

DS2505
SILICON LABEL DESCRIPTION
The DS2505 16Kb 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
16Kb of user-programmable EPROM. The power to program and read the DS2505 is derived entirely
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from the 1-Wire
communication line. Data is transferred serially via the 1-Wire protocol which requires
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A provision is also included for indicating that a certain page or pages of data are no longer valid and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
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