DS2404

11 of 28

020998

Read Memory [F0h]

The read memory command may be used to read the entire memory. After issuing the command, the user

must provide the 2-byte target address. After the two bytes, the user reads data beginning from the target

address and may continue until the end of memory, at which point logic 1’s will be read. It is important to

realize that the target address registers will contain the address provided. The ending offset/data status

byte is unaffected.

The hardware of the DS2404 provides a means to accomplish error-free writing to the memory section.

To safeguard reading data in the 1-Wire environment and to simultaneously speed up data transfers, it is

recommended to packetize data into data packets of the size of one memory page each. Such a packet

would typically store a 16-bit CRC with each page of data to ensure rapid, error-free data transfers that

eliminate having to read a page multiple times to determine if the received data is correct or not. (See the

Book of DS19xx iButton Standards, Chapter 7 for the recommended file structure to be used with the 1-

Wire environment.)

MEMORY FUNCTION EXAMPLES

Example 1: Write one page of data to page 15

Read page 15 (3-wire port)

MASTER MODE

DATA(LSB FIRST)

COMMENTS

TX

Reset

TX

0Fh

Issue “write scratchpad” command

TX

E0h

TA1, beginning offset=0

TX

01h

TA2, address=01E0h

TX

<32 data bytes>

Write 1 page of data to scratchpad

TX

Reset

TX

AAh

Issue “read scratchpad” command

RX

E0h

Read TA1, beginning offset=0

RX

01h

Read TA2, address=01E0h

RX

1Fh

Read E/S, ending offset=31d, flags=0

RX

<32 data bytes>

Read scratchpad data and verify

TX

Reset

TX

55h

Issue “copy scratchpad” command

TX

E0h

TX

01h

TX

1Fh

TA1

TA2

AUTHORIZATION CODE

E/S

RX

<busy indicator>

Wait until DQ=0 (~30

µs typical)

TX

Reset

TX

F0h

Issue “read memory” command

TX

E0h

TA1, beginning offset=0

TX

01h

TA2, address=01E0h

RX

<32 data bytes>

Read memory page 15 and verify

TX

Reset

device expects to receive a memory function command.