Rainbow Electronics DS2502 User Manual

12365

4

DS2502

1 kbit Add-Only Memory

www.dalsemi.com

GND

DATA

NC

BOTTOM VIEW

TO-92

2

3

1

FEATURES

§ 1024 bits Electrically Programmable Read

Only Memory (EPROM) communicates with
the economy of one signal plus ground

§ Unique, factory-lasered and tested 64-bit

registration number (8-bit family code + 48­bit serial number + 8-bit CRC tester) assures
absolute traceability because no two parts are
alike

§ Built-in multidrop controller ensures

compatibility with other MicroLAN products

§ EPROM partitioned into four 256-bit pages

for randomly accessing packetized data

§ Each memory page can be permanently

write-protected to prevent tampering

§ Device is an “add only” memory where

additional data can be programmed into
EPROM without disturbing existing data

§ Architecture allows software to patch data by

superseding an old page in favor of a newly
programmed page

§ Reduces control, address, data, power, and

programming signals to a single data pin

§ Directly connects to a single port pin of a

microprocessor and communicates at up to

16.3 kbits per second

§ 8-bit family code specifies DS2502

communications requirements to reader

§ Presence detector acknowledges when the

reader first applies voltage

§ Low cost TO-92 or 8-pin SOIC and TSOC

surface mount package

§ Reads over a wide voltage range of 2.8V to

6.0V from -40°C to +85°C; programs at

11.5V to 12.0V from -40°C to +50°C

PIN ASSIGNMENT

1

8

NC

7

NC

6

NC

5

NC

NC
NC
NC

DS2502

NC

2

NC

DATA

GND

8-PIN SOIC (150 MIL)

GND

DATA

3
4

TSOC PACKAGE

NC

TOP VIEW

3.7 X 4.0 X 1.5 mm
See Mech.

Drawings Section

ORDERING INFORMATION

DS2502 TO-92 package
DS2502S 8-pin SOIC package
DS2502P 6-pin TSOC package
DS2502T Tape & Reel version of DS2502
DS2502Y Tape & Reel version of DS2502S
DS2502V Tape & Reel version of DS2502P
DS2502X1 Chip Scale Pkg., Tape & Reel

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DS2502

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 interface­for 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-WireTM 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 1­Wire 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

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DS2502

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 DS2502 are not accessible until the ROM function
protocol has been satisfied. This protocol is described in the ROM functions flow chart (Figure 9). The 1­Wire bus master must first provide one of four ROM function commands: 1) Read ROM, 2) Match ROM,

3) Search ROM, or 4) Skip ROM. After a ROM function sequence has been successfully executed, the
bus master may then provide any one of the memory function commands specific to the DS2502 (Figure

6).
The 1-Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Figure 4

shows a hardware implementation of this CRC generator. Additional information about the Dallas
Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book of DS19xx iButton Standards.
The shift register acting as the CRC accumulator is initialized to 0. Then starting with the least significant
bit of the family code, 1 bit at a time is shifted in. After the 8th bit of the family code has been entered,
then the serial number is entered. After the 48th bit of the serial number has been entered, the shift
register contains the CRC value. Shifting in the 8 bits of CRC should return the shift register to all 0s.

DS2502 BLOCK DIAGRAM Figure 1

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HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2

DS2502

64-BIT LASERED ROM Figure 3

8–Bit CRC Code 48–Bit Serial Number 8–Bit Family Code (09h)

MSB LSB MSB LSB MSB LSB

1-WIRE CRC GENERATOR Figure 4

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DS2502

1024-BITS EPROM

The memory map in Figure 5 shows the 1024-bit EPROM section of the DS2502 which is configured as
four pages of 32 bytes each. The 8-bit scratchpad is an additional register that acts as a buffer when
programming the memory. Data is first written to the scratchpad and then verified by reading an 8-bit
CRC from the DS2502 that confirms proper receipt of the data. If the buffer contents are correct, a
programming voltage should be applied and the byte of data will be written into the selected address in
memory. This process ensures data integrity when programming the memory. The details for reading and
programming the 1024-bit EPROM portion of the DS2502 are given in the Memory Function Commands
section.

EPROM STATUS BYTES

In addition to the 1024 bits of data memory the DS2502 provides 64 bits of Status Memory accessible
with separate commands.

The EPROM Status Bytes can be read or programmed to indicate various conditions to the software
interrogating the DS2502. The first byte of the EPROM Status Memory contain the Write Protect Page
bits which inhibit programming of the corresponding page in the 1024-bit main memory area if the
appropriate write protection bit is programmed. Once a bit has been programmed in the Write Protect
Page byte, the entire 32-byte page that corresponds to that bit can no longer be altered but may still be
read.

The next 4 bytes of the EPROM Status Memory contain the Page Address Redirection Bytes, which
indicate if one or more of the pages of data in the 1026-bit EPROM section have been invalidated and
redirected to the page address contained in the appropriate redirection byte. The hardware of the DS2502
makes no decisions based on the contents of the Page Address Redirection Bytes. These additional bytes
of Status EPROM technology, bits within a page can be changed from a logical 1 to a logical 0 by
programming, but cannot be changed back. Therefore, it is not possible to simply rewrite a page if the
data requires changing or updating, but with space permitting, an entire page of data can be redirected to
another page within the DS2502 by writing the one’s complement of the new page address into the Page
Address Redirection Byte that corresponds to the original (replaced) page.

This architecture allows the user’s software to make a “data patch” to the EPROM by indicating that a
particular page or pages should be replaced with those indicated in the Page Address Redirection Bytes.

If a Page Address Redirection Byte has an FFH value, the data in the main memory that corresponds to
that page is valid. If a Page Address Redirection Byte has some other hex value, the data in the page
corresponding to that redirection byte is invalid, and the valid data can now be found at the one’s
complement of the page address indicated by the hex value stored in the associated Page Address
Redirection Byte. A value of FDH in the redirection byte for page 1, for example, would indicate that the
updated data is now in page 2. The details for reading and programming the EPROM status memory
portion of the DS2502 are given in the Memory Function Commands section.

MEMORY FUNCTION COMMANDS

The “Memory Function Flow Chart” (Figure 6) describes the protocols necessary for accessing the
various data fields within the DS2502. The Memory Function Control section, 8-bit scratchpad, and the
Program Voltage Detect circuit combine to interpret the commands issued by the bus master and create
the correct control signals within the device. A 3-byte protocol is issued by the bus master. It is
comprised of a command byte to determine the type of operation and two address bytes to determine the
specific starting byte location within a data field. The command byte indicates if the device is to be read

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or written. Writing data involves not only issuing the correct command sequence by also providing a 12­volt programming voltage at the appropriate times. To execute a write sequence, a byte of data is first
loaded into the scratchpad and then programmed into the selected address. Write sequences always occur
a byte at a time. To execute a read sequence, the starting address is issued by the bus master and data is
read from the part beginning at that initial location and continuing to the end of the selected data field or
until a reset sequence is issued. All bits transferred to the DS2502 and received back by the bus master
are sent least significant bit first.

DS2502 MEMORY MAP Figure 5

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MEMORY FUNCTION FLOW CHART Figure 6

DS2502

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