Rainbow Electronics DS2404 - Manual (Page 11)

DS2404
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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 Master pulses RST low
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 Master pulses RST low
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 Master pulses RST low
TX 55h Issue “copy scratchpad” command
TX E0h
TX 01h
TX 1Fh
TA1
TA2
AUTHORIZATION CODE
E/S
RX Wait until DQ=0 (~30 ms typical)
TX Reset Master pulses RST low
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 Master pulses RST low, done
NOTE: The ROM function commands do not apply to the 3-wire port. After RST is at a high level, the
device expects to receive a memory function command.