DS2422 Maxim, DS2422 Datasheet - Page 27

• 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

DS2422
COPY SCRATCHPAD WITH PASSWORD [99h]
This command is used to copy data from the scratchpad to the writable memory sections. After issuing the Copy
Scratchpad command, the master must provide a 3-byte authorization pattern, which can be obtained by reading
the scratchpad for verification. This pattern must exactly match the data contained in the three address registers
(TA1, TA2, E/S, in that order). Next the master must transmit the 64-bit full-access password. If passwords are
enabled and the transmitted password is different from the stored full-access password, the Copy Scratchpad with
Password command will fail. The device will stop communicating and will wait for a reset pulse. If the password
was correct or if passwords were not enabled, the device will test the 3-byte authorization code. If the authorization
code pattern matches, the AA (Authorization Accepted) flag will be set and the copy will begin. A pattern of
alternating 1s and 0s will be transmitted after the data has been copied until the master issues a reset pulse. While
the copy is in progress any attempt to reset the part will be ignored. Copy typically takes 2µs per byte.
The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset
through the ending offset will be copied, starting at the target address. Anywhere from 1 to 32 bytes may be copied
to memory with this command. The AA flag will remain at logic 1 until it is cleared by the next Write Scratchpad
command. With suitable password, the copy scratchpad will always function for the 16 pages of data memory and
the 2 pages of calibration memory. While a mission is in progress, write attempts to the register pages will not be
successful. The AA bit (Authorization Accepted) remaining at 0 will indicate this.
READ MEMORY WITH PASSWORD AND CRC [69h]
The Read Memory with CRC command is the general function to read from the device. This command generates
and transmits a 16-bit CRC following the last data byte of a memory page.
After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte
address that indicates a starting byte location. Next the master must transmit one of the 64-bit passwords. If
passwords are enabled and the transmitted password does not match one of the stored passwords, the Read
Memory with Password and CRC command will fail. The device will stop communicating and will wait for a reset
pulse. If the password was correct or if passwords were not enabled, the master reads data from the DS2422
beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus
master will send 16 additional read data time slots and receive the inverted 16-bit CRC. With subsequent read data
time slots the master will receive data starting at the beginning of the next memory page followed again by the
CRC for that page. This sequence will continue until the bus master resets the device. When trying to read the
passwords or memory areas that are marked as "reserved", the DS2422 will transmit 00h or FFh bytes
respectively. The CRC at the end of a 32-byte memory page is based on the data as it was transmitted.
With the initial pass through the Read Memory with CRC flow, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator followed by the 2 address bytes and the contents of the data
memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result
of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of
the last page is read, the bus master will receive logical 1s from the DS2422 until a reset pulse is issued. The Read
Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
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