Rainbow Electronics DS75LV - Manual (Page 11)

DS75LV: Digital Thermometer and Thermostat
11 of 13
Software POR—The soft power on reset (POR) command is 54h. The master sends a START followed by an
address byte containing the DS75LV bus address. The R/W bit must be a 0. The DS75LV will respond with an
ACK. If the next byte is a 0x54, the DS75LV will reset as if power had been cycled. No ACK will be send by the IC
after the POR command is received.
Reading from the DS75LV—When reading from the DS75LV, if the pointer was already pointed to the desired
register during a previous transaction, the read can be performed immediately without changing the pointer setting.
In this case the master sends a START followed by an address byte containing the DS75LV bus address. The R/W
bit must be a 1, which tells the DS75LV that a read is being performed. After the DS75LV sends an ACK in
response to the address byte, the DS75LV will begin transmitting the requested data on the next clock cycle. When
reading from the configuration register, the DS75LV will transmit one byte of data, after which the master must
respond with a NACK followed by a STOP (see Figure 9e). For two-byte reads (i.e., from the Temperature, T
OS
or
T
HYST
register), the DS75LV will transmit two bytes of data, and the master must respond to the first data byte with
an ACK and to the second byte with a NACK followed by a STOP (see Figure 9a). If only the most significant byte
of data is needed, the master can issue a NACK followed by a STOP after reading the first data byte in which case
the transaction will be the same as for a read from the configuration register.
If the pointer is not already pointing to the desired register, the pointer must first be updated as shown in Figure 9d,
which shows a pointer update followed by a single-byte read. The value of the R/W bit in the initial address byte is
a 0 (“write”) since the master is going to write a pointer byte to the DS75LV. After the DS75LV responds to the
address byte with an ACK, the master sends a pointer byte that corresponds to the desired register. The master
must then perform a repeated start followed by a standard one or two byte read sequence (with R/W =1) as
described in the previous paragraph.
Bus Timeout—The DS75LV has a bus timeout feature that prevents communication errors from leaving the IC in a
state where SDA is held low disrupting other devices on the bus. If the DS75LV holds the SDA line low for a period
of t
TIMEOUT
, its bus interface will automatically reset and release the SDA line. Bus communication frequency must
be fast enough to prevent a reset during normal operation. The bus timeout feature only applies to when the
DS75LV is holding SDA low. Other devices can hold SDA low for an undefined period without causing the interface
to reset.