Rainbow Electronics DS75LV - Manual (Page 10)

DS75LV: Digital Thermometer and Thermostat
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Address Byte: The control byte is transmitted by the master and consists of the 7-bit slave address plus a
read/write (R/W
¯¯) bit (see Figure 7). If the master is going to read data from the slave device then R/W ¯¯ = 1, and if
the master is going to write data to the slave device then R/W ¯¯ = 0.
Pointer Byte: The pointer byte is used by the master to tell the DS75LV which register is going to be accessed
during communication. The six MSbs of the pointer byte (see Figure 8) are always 0 and the two LSbs correspond
to the desired register as shown in Table 7.
Figure 6. Start, Stop, and ACK Signals
Figure 7. Address Byte
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
1 0 0 1 A
2
A
1
A
0 R/W ¯¯
Figure 8. Pointer Byte
bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
0 0 0 0 0 0 P1 P0
GENERAL 2-WIRE INFORMATION
§ All data is transmitted MSb first over the 2-wire bus.
§ One bit of data is transmitted on the 2-wire bus each SCL period.
§ A pullup resistor is required on the SDA line and, when the bus is idle, both SDA and SCL must remain in a logic-
high state.
§ All bus communication must be initiated with a START condition and terminated with a STOP condition. During a
START or STOP is the only time SDA is allowed to change states while SCL is high. At all other times, changes
on the SDA line can only occur when SCL is low: SDA must remain stable when SCL is high.
§ After every 8-bit (1-byte) transfer, the receiving device must answer with an ACK (or NACK), which takes one
SCL period. Therefore, nine clocks are required for every one-byte data transfer.
Writing to the DS75LV— To write to the DS75LV, the master must generate a START followed by an address
byte containing the DS75LV bus address. The value of the R/W bit must be a 0, which indicates that a write is
about to take place. The DS75LV will respond with an ACK after receiving the address byte. The master then
sends a pointer byte which tells the DS75LV which register is being written to. The DS75LV will again respond with
an ACK after receiving the pointer byte. Following this ACK the master device must immediately begin transmitting
data to the DS75LV. When writing to the configuration register, the master must send one byte of data (see Figure
9b), and when writing to the T
OS
or T
HYST
registers the master must send two bytes of data (see Figure 9c). After
receiving each data byte, the DS75LV will respond with an ACK, and the transaction is finished with a STOP from
the master.
SCL
SDA
START
Condition
STOP
Condition
…
…
ACK (or NACK)
From Receiver