Rainbow Electronics DS75LX - Manual (Page 10)

DS75LX: Digital Thermometer and Thermostat with Extended Addressing
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Figure 5. Start, Stop, and ACK Signals
Figure 6. Address Byte
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
a
6
a
5
a
4
a
3
a
2
a
1
a
0
R/W ¯¯
The Address Pins A0–A2 are tri-state inputs. These can be low, high, or floating in any combination, resulting in 27
address possibilities. These map into the address byte according to Table 6.
Figure 7. 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
ƒ All data is transmitted MSb first over the 2-wire bus.
ƒ One bit of data is transmitted on the 2-wire bus each SCL period.
ƒ 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.
ƒ 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.
ƒ 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 1-byte data transfer.
SCL
SDA
START
Condition
STOP
Condition
…
…
ACK (or NACK)
From Receiver