Rainbow-electronics DS2404 Manual do Utilizador descarregar pdf (Página 11)

DS2404

11 of 29

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 <busy indicator>

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.

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