Rainbow Electronics DS2502 - Manual (Page 2)

DS2502
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SILICON LABEL DESCRIPTION
The DS2502 1 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 DS2502 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 (09h) plus 1
kbit of EPROM which is user-programmable. The power to program and read the DS2502 is derived
entirely from the 1-Wire
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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that a certain page or pages of data are no longer valid and have been replaced with new or updated data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 stand-alone database. The 48-bit serial number that is
factory-lasered into each DS2502 provides a guaranteed unique identity which allows for absolute
traceability. The familiar TO-92 or SOIC or 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 DS2502. The DS2502 has three main data components: 1) 64-bit lasered ROM, 2) 1024-bit EPROM,
and 3) EPROM Status Bytes. 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
DS2502 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 six 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 9. After a ROM Function
Command is successfully executed, the memory functions that operate on the EPROM portions of the
DS2502 become accessible and the bus master may issue any one of the five Memory Function
Commands specific to the DS2502 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 DS2502 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 DS2502 to operate as a 1-Wire device and