Rainbow Electronics DS28EA00 - Manual (Page 10)

DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
10 of 29
Registration number is read, it is put into the chain DONE state, which enables the next device in the chain to
respond to the Conditional Read ROM command.
At the beginning of the sequence discovery process all devices are put into the chain ON state. As the discovery
progresses, one device after another is transitioned into the DONE state until all devices are identified. Finally, all
devices are put into the chain OFF state, which releases the PIOs and restores their power-on default state.
CONTROL FUNCTION COMMANDS
The Control Function Flow Chart (Figure 10) describes the protocols necessary for measuring temperatures,
accessing the memory and PIOs, and changing the chain state. Examples on how to use these and other functions
are included at the end of this document. The communication between master and DS28EA00 takes place either at
standard speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive mode after
power-up the DS28EA00 communicates at standard speed.
WRITE SCRATCHPAD [4Eh]
This command allows the master to write 3 bytes of data to the scratchpad of the DS28EA00. The first data byte is
associated with the TH register (byte address 2), the second byte is associated with the TL register (byte address
3), and the third byte is associated with the configuration register (byte address 4). Data must be transmitted least
significant bit first. All three bytes MUST be written before the master issues a reset, or the data may be corrupted.
READ SCRATCHPAD [BEh]
This command allows the master to read the contents of the scratchpad. The data transfer starts with the least
significant bit of the temperature readout register at byte address 0 and continues through the remaining 7 bytes of
the scratchpad. If the master continues reading, it gets a 9
th
byte, which is an 8-bit CRC of all the data in the
scratchpad. This CRC is generated by the DS28EA00 and uses the same polynomial function as is used with the
ROM Registration Number. The CRC is transmitted in its true (non-inverted) form. The master may issue a reset to
terminate the reading early if only part of the scratchpad data is needed.
COPY SCRATCHPAD [48h]
This command copies the contents of the scratchpad byte addresses 2 to 4 (TH, TL and configuration registers) to
the back-up EEPROM. If the device has no V
DD
power, the master must enable a strong pullup on the 1-Wire bus
for the duration of t
PROGMAX
within 10µs after this command is issued. If the device is powered through the V
DD
pin,
the master may generate read time slots to monitor the copy process. Copy is completed when the master reads 1-
bits instead of 0-bits.
CONVERT TEMPERATURE [44h]
This command initiates a temperature conversion. Following the conversion, the resulting thermal data is found in
the temperature readout register in the scratchpad and the DS28EA00 returns to its low-power idle state. If the
device has no V
DD
power, the master must enable a strong pullup on the 1-Wire bus for the duration of the applica-
ble resolution-dependent t
CONVMAX
within 10µs after this command is issued. If the device is powered through the
V
DD
pin, the master may generate read time slots to monitor the conversion process. The conversion is completed
when the master reads 1-bits instead of 0-bits.
READ POWER MODE [B4h]
For Copy Scratchpad and Convert Temperature the master needs to know whether the DS28EA00 has V
DD
power
available. The Read Power Mode command is implemented to provide the master with this information. After the
command code, the master issues read time slots. If the master reads 1’s, the device is powered through the V
DD
pin. If the device is powered through the 1-Wire line, the master will read 0’s. The power supply sensor samples the
state of the V
DD
pin for every time slot that the master generates after the command code.