DS9101 datasheet(21/42 Pages) MAXIM

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Read Scratchpad [AAh]

This command is used to verify scratchpad data and

target addresses. After issuing the Read Scratchpad

command, the master begins reading. The first 2 bytes

are the target address. The next byte is the ending off-

set/data status byte (E/S) followed by the scratchpad

data beginning at the byte offset T[4:0], as shown in

Figure 9. Regardless of the actual ending offset, the

master can read data until the end of the scratchpad

after which it receives an inverted CRC-16 of the com-

mand code, target addresses TA1 and TA2, the E/S

byte, and the scratchpad data starting at the target

address. After the CRC is read, the bus master reads

logical “1”s from the DS1921G until a reset pulse is

issued.

Copy Scratchpad [55h]

This command is used to copy data from the scratch-

pad to the writable memory sections. Applying a Copy

Scratchpad command to the Sample Rate register can

start a mission provided that several preconditions are

met. See the

Mission Start and Logging Process sec-

tion and the flowchart in Figure 11 for details. After issu-

ing the Copy Scratchpad command, the master must

provide a 3-byte authorization pattern, which can be

obtained by reading the scratchpad for verification.

This pattern must exactly match the data contained in

the three address registers (TA1, TA2, E/S, in that

order). If the pattern matches, the AA flag is set and the

copy begins. A pattern of alternating “1”s and “0”s is

transmitted after the data has been copied until the

master issues a reset pulse. While the copy is in

progress, any attempt to reset the part is ignored. Copy

typically takes 2µs per byte.

The data to be copied is determined by the three

address registers. The scratchpad data from the begin-

ning offset through the ending offset is copied, starting

at the target address. Anywhere from 1 to 32 bytes can

be copied to memory with this command. The AA flag

remains at logic 1 until it is cleared by the next Write

Scratchpad command. Note that the Copy Scratchpad

command, when applied to the address range 200h to

213h during a mission, ends the mission.

Read Memory [F0h]

The Read Memory command can be used to read the

entire memory. After issuing the command, the master

must provide the 2-byte target address. After the 2

bytes, the master reads data beginning from the target

address and can continue until the end of memory, at

which point logic “0”s are read. It is important to realize

that the target address registers contain the address

provided. The ending offset/data status byte is unaf-

fected.

The hardware of the DS1921G provides a means to

accomplish error-free writing to the memory section. To

safeguard data in the 1-Wire environment when read-

ing 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 elim-

inate having to read a page multiple times to verify if

the received data is correct (refer to Application Note

114:

1-Wire File Structure for the recommended file

structure).

Thermochron iButton

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