DS9101 datasheet(28/55 Pages) MAXIM

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Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

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The last step to begin a mission is to issue the Start

Mission command. As soon as it has received this com-

mand, the DS1923 sets the MIP flag and clears the

MEMCLR flag. With the immediate/delayed start mode

(SUTA = 0), after as many minutes as specified by the

Mission Start Delay are over, the device wakes up,

copies the current date and time to the Mission

Timestamp register, and logs the first entry of the mis-

sion. This increments both the Mission Samples

Counter and Device Samples Counter. All subsequent

log entries are made as specified by the value in the

Sample Rate register and the EHSS bit.

If the start upon temperature alarm mode is chosen

(SUTA = 1) and temperature logging is enabled (ETL =

1), the DS1923 first waits until the start delay is over.

Then the device wakes up in intervals as specified by

the sample rate and EHSS bit and measures the tem-

perature. This increments the Device Samples Counter

when the temperature alarm occurred. However, the

Mission Samples Counter does not increment. One

sample period later the Mission Timestamp register is

set. From then on, both the Mission Samples Counter

and Device Samples Counter registers increment at the

same time. All subsequent log entries are made as

specified by the value in the Sample Rate register and

the EHSS bit.

The general-purpose memory operates independently of

the other memory sections and is not write protected

during a mission. All the DS1923’s memory can be read

at any time, e.g., to watch the progress of a mission.

Attempts to read the passwords read 00h bytes instead

of the data that is stored in the password registers.

Memory Access

Address Registers and Transfer Status

Because of the serial data transfer, the DS1923

employs three address registers called TA1, TA2, and

E/S (Figure 8). 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 trans-

fer status register. It is used to verify data integrity with

write commands. Therefore, the master only has 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. The DS1923 requires that the ending offset is

always 1Fh for a Copy Scratchpad to function. 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 determine the

address within the scratchpad, where intermediate

storage of data begins. This address is called byte off-

set. If the target address for a Write Scratchpad com-

mand is 13Ch, for example, the scratchpad stores

incoming data beginning at the byte offset 1Ch and is

full after only 4 bytes. The corresponding ending offset

in this example is 1Fh. For best economy of speed and

BIT NUMBER

TARGET ADDRESS (TA1)

TARGET ADDRESS (TA2)

T15

T14

T13

T12

T11

T10

ENDING ADDRESS WITH

DATA STATUS (E/S)

(READ ONLY)

Figure 8. Address Registers

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