DS9101 datasheet(29/55 Pages) MAXIM

29 / 55 page

efficiency, the target address for writing should point to

the beginning of a page, i.e., the byte offset is 0. Thus,

the full 32-byte capacity of the scratchpad is available,

resulting also in the ending offset of 1Fh. The ending

offset together with the PF flag are a means to support

the master checking the data integrity after a Write

Scratchpad command. The highest valued bit of the

E/S register, called authorization accepted (AA), indi-

cates that a valid Copy Scratchpad command for the

scratchpad has been received and executed. Writing

data to the scratchpad clears this flag.

Writing with Verification

To write data to the DS1923, the scratchpad must be

used as intermediate storage. First, the master issues

the Write Scratchpad command to specify the desired

target address, followed by the data to be written to the

scratchpad. In the next step, the master sends the

Read Scratchpad command to read the scratchpad

and to verify data integrity. As preamble to the scratch-

pad data, the DS1923 sends the requested target

address TA1 and TA2 and the contents of the E/S

rectly in the scratchpad. The master does not need to

continue reading; it can start a new trial to write data to

the scratchpad. Similarly, a set AA flag indicates that

the Write Scratchpad command was not recognized by

the device. If everything went correctly, both flags are

cleared and the ending offset indicates the address of

the last byte written to the scratchpad. Now the master

can continue verifying every data bit. After the master

has verified the data, it must send the Copy Scratchpad

command. This command must be followed exactly by

the data of the three address registers TA1, TA2, and

E/S, as the master has read them verifying the scratch-

pad. As soon as the DS1923 has received these bytes,

it copies the data to the requested location beginning

at the target address.

Memory and Control

Function Commands

Figure 9 shows the protocols necessary for accessing

the memory and the special function registers of the

DS1923. An example on how to use these and other

functions to set up the DS1923 for a mission is included

in the

Mission Example: Prepare and Start a New

Mission section. The communication between the mas-

ter and the DS1923 takes place either at standard

speed (default, OD = 0) or at overdrive speed (OD =

1). If not explicitly set into the overdrive mode, the

DS1923 assumes standard speed. Internal memory

access during a mission has priority over external

access through the 1-Wire interface. This affects sever-

al commands in this section. See the

Memory Access

Conflicts section for details and solutions.

Write Scratchpad [0Fh]

After issuing the Write Scratchpad command, the mas-

ter must first provide the 2-byte target address, fol-

lowed by the data to be written to the scratchpad. The

data is written to the scratchpad starting at the byte off-

set T[4:0]. The master must send as many bytes as are

needed to reach the ending offset of 1Fh. If a data byte

is incomplete, its content is ignored and the partial byte

flag PF is set.

When executing the Write Scratchpad command, the

CRC generator inside the DS1923 calculates a CRC of

the entire data stream, starting at the command code

and ending at the last data byte sent by the master

(Figure 15). This CRC is generated using the CRC-16

polynomial by first clearing the CRC generator and then

shifting in the command code (0Fh) of the Write

Scratchpad command, the target addresses TA1 and

TA2 as supplied by the master, and all the data bytes.

If the ending offset is 11111b, the master can send 16

read time slots and receive the inverted CRC-16 gener-

ated by the DS1923.

Note that both register pages are write protected dur-

ing a mission. Although the Write Scratchpad command

works normally at any time, the subsequent copy

scratchpad to a register page fails during a mission.

Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

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