DS2422 Maxim, DS2422 Datasheet - Page 25

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

If there is a risk of unauthorized access to the DS2422 or manipulation of data, one should define passwords for
read access and full access. Before the passwords become effective, their use needs to be enabled. See Security
by Password for more details.
The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command,
the DS2422 sets the MIP flag and clear 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, copy the current date
and time to the mission time stamp register, and log the first entry of the mission. 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
delay is over. Then the device wakes up in intervals as specified by the sample rate and EHSS bit and measure the
temperature. This increments the device samples counter only. The first sample of the mission is logged when the
temperature alarm occurred. However, the Mission Sample 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 increments 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 memory of the DS2422 can be read at any time, e. g., to watch the progress of a mission.
Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.
ADDRESS REGISTERS AND TRANSFER STATUS
Because of the serial data transfer, the DS2422 employs three address registers, called TA1, TA2, and E/S (Figure
11). 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 command. 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 only has read access to this register. The
lower 5 bits of the E/S Register indicate the address of the last byte that has been written to the scratchpad. This
address is called Ending Offset. The DS2422 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 will begin. This
address is called byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad
will store incoming data beginning at the byte offset 1Ch and will be full after only 4 bytes. The corresponding
ending offset in this example is 1Fh. For best economy of speed and efficiency, the target address for writing
should point to the beginning of a new page, i.e., the byte offset will be 0. Thus the full 32-byte capacity of the
scratchpad is available, resulting also in the ending offset of 1Fh. However, it is possible to write 1 or several
contiguous bytes somewhere within a page. The ending offset together with the Partial and Overflow Flag is mainly
a means to support the master checking the data integrity after a Write command. The highest valued bit of the E/S
Register, called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been
received and executed. Writing data to the scratchpad clears this flag.
Figure 11. Address Registers
Target Address (TA1)
Target Address (TA2)
Ending Address with
Data Status (E/S)
(Read Only)
Bit #
T15
AA
T7
7
T14
T6
6
0
T13
PF
T5
5
T12
T4
E4
4
25 of 49
T11
T3
E3
3
,
ETL = 1) the DS2422 will first wait until the start
T10
T2
E2
2
T1
T9
E1
1
T0
T8
E0
0