DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 26

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

The general-purpose memory operates independently of the other memory sections and is not write-protected
during a mission. All memory of the DS1922L/T 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 DS1922L/T 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 are written or from
which data are 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 DS1922L/T 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 offset. If the target address for a Write command is 13Ch, for example, then the scratchpad
stores 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 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. The ending offset together with the PF 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 8. Address Registers
WRITING WITH VERIFICATION
To write data to the DS1922L/T, the scratchpad has to 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 scratchpad data, the DS1922L/T sends the requested target address TA1 and
TA2 and the contents of the E/S Register. 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 Write 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 has to 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 scratchpad. As soon as the DS1922L/T has received these bytes, it
copies the data to the requested location beginning at the target address.
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
E4
T4
4
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T11
T3
E3
3
T10
E2
T2
2
T1
T9
E1
1
E0
T0
T8
0
DS1922L/DS1922T