DS1921H/Z Maxim Integrated Products, DS1921H/Z Datasheet - Page 16

• Manufacturer Part Number: DS1921H/Z
• Description: High Resolution Thermochron Ibutton Range H
• Manufacturer: Maxim Integrated Products

DS1921H/Z
MEMORY FUNCTION COMMANDS
The Memory Function Flow Chart (Figure 10) describes the protocols necessary for accessing the
memory and the special function registers of the DS1921H/Z. An example on how to use these and other
functions to set up the DS1921H/Z for a mission is included at the end of this document, preceding the
Electrical Characteristics section. The communication between master and DS1921H/Z takes place
either at regular speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the
Overdrive mode, the DS1921 assumes regular speed.
Write Scratchpad Command [0Fh]
After issuing the Write Scratchpad command, the master must first provide the 2-byte target address,
followed by the data to be written to the scratchpad. The data will be written to the scratchpad starting at
the byte offset (T4:T0). The ending offset (E4:E0) will be the byte offset at which the master stops writ-
ing data. Only full data bytes are accepted. If the last data byte is incomplete, its content will be ignored
and the partial byte flag (PF) will be set.
When executing the Write Scratchpad command, the CRC generator inside the DS1921H/Z (see Figure
15) calculates a CRC of the entire data stream, starting at the command code and ending at the last data
byte sent by the master. This CRC is generated using the CRC16 polynomial by first clearing the CRC
generator and then shifting in the command code (0Fh) of the Write Scratchpad command, the Target
Addresses TA1 and TA2 as supplied by the master and all the data bytes. The master may end the Write
Scratchpad command at any time. However, if the ending offset is 11111b, the master may send 16 read
time slots and will receive the CRC generated by the DS1921H/Z.
The range 200h to 213h of the register page is write-protected during a mission. See Figure 6, Register
Page Map, for the access type of the individual registers between and during missions.
Read Scratchpad Command [AAh]
This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad
command, the master begins reading. The first 2 bytes will be the target address. The next byte will be the
ending offset/data status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0),
as shown in Figure 9. Regardless of the actual ending offset, the master may read data until the end of the
scratchpad after which it will receive a CRC16 of the command code, Target Addresses TA1 and TA2,
the E/S byte, and the scratchpad data starting at the target address. After the CRC is read, the bus master
will read logical 1s from the DS1921H/Z until a reset pulse is issued.
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