DS9101 datasheet(19/42 Pages) MAXIM

19 / 42 page

Next, the low temperature and high temperature thresh-

olds that specify the temperature tolerance band must

be defined. The

Temperature Conversion section

describes how to convert a temperature value into the

binary code to be written to the threshold registers.

The state of the search condition bits in the Control

are connected to form a 1-Wire net, the setting of the

search condition enables these devices to participate

in the conditional search if certain events, such as

timer or temperature alarms, have occurred. Details

on the search conditions are found in the

ROM

Function Commands section and in the Control regis-

ter description.

The setting of the rollover-enable bit (RO) and sample

rate depends on the duration of the mission and the

monitoring requirements. If the most recent temperature

history is important, the rollover should be enabled

(RO = 1). Otherwise, one should estimate the duration

of the mission in minutes and divide the number by

2048 to calculate the value of the sample rate (number

of minutes between temperature conversions). For

example, if the estimated duration of a mission is 10

days (14,400min), then the 2048-byte capacity of the

data-log memory would be sufficient to store a new

value every 7min. If the DS1921G’s data-log memory is

not large enough to store all temperature readings, one

can use several devices and set the Mission Start Delay

to values that make the second device start recording

as soon as the memory of the first device is full and so

on. The RO bit needs to be set to 0 to disable rollover

that would otherwise overwrite the recorded tempera-

ture log.

After the RO bit and the Mission Start Delay are set, the

Sample Rate register is the last element of data that is

written. The sample rate can be any value from 1 to

255, coded as an unsigned 8-bit binary number. As

soon as the sample rate is written, the DS1921G sets

the MIP flag and clears the MEMCLR flag. After as

many minutes as specified by the Mission Start Delay

are over, the device waits for the next minute boundary,

then wakes up, copies the current time and date to the

Mission Timestamp register, and makes the first tem-

perature conversion of the mission. This increments

both the Mission Samples Counter and Device Samples

Counter. All subsequent temperature measurements

are taken on minute boundaries specified by the value

in the Sample Rate register. One can read the memory

of the DS1921G to watch the mission as it progresses.

Care should be taken to avoid memory access con-

flicts. See the

Memory Access Conflicts section for

details.

Address Registers and

Transfer Status

Because of the serial data transfer, the DS1921G

employs three address registers, called TA1, TA2, and

E/S (Figure 9). Registers TA1 and TA2 must be loaded

with the target address to which the data is written or

from which data is sent to the master upon a read com-

mand. Register E/S acts like a byte counter and transfer

status register. It is used to verify data integrity with

write commands. Therefore, the master has only read

access to this register. The lower 5 bits of the E/S regis-

ter indicate the address of the last byte that has been

written to the scratchpad. This address is called Ending

Offset. Bit 5 of the E/S register, called PF or partial byte

flag, is set if the number of data bits sent by the master

is not an integer multiple of 8. Bit 6 is always a 0. Note

that the lowest 5 bits of the target address also deter-

mine the address within the scratchpad where interme-

diate storage of data begins. This address is called

byte offset. If the target address for a write command is

13Ch, for example, then the scratchpad stores incom-

ing data beginning at the byte offset 1Ch and is full

after only 4 bytes. The corresponding ending offset in

this example is 1Fh. For the best economy of speed

and efficiency, the target address for writing should

point to the beginning of a new page, i.e., the byte off-

set is 0. Thus, the full 32-byte capacity of the scratch-

pad is available, resulting also in the ending offset of

1Fh. However, it is possible to write one or several con-

tiguous bytes somewhere within a page. The ending

offset together with the partial and overflow flag are a

means to support the master checking the data integri-

ty after a write command. The highest valued bit of the

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

cates that a valid copy 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 DS1921G, 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 DS1921G sends the requested target

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

ter. If the PF flag is set, data did not arrive correctly 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

Thermochron iButton

______________________________________________________________________________________

DS9101 Datasheet(PDF) 19 Page - Maxim Integrated Products

DS9101 Datasheet(HTML) 19 Page - Maxim Integrated Products

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42

Datasheet Download

Link URL