Rainbow Electronics DS1857 - Manual (Page 21)

DS1857
Dual Temperature-Controlled Resistors with
External Temperature Input and Monitors
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data is transmitted on SDA by the DS1857, while
the serial clock is input on SCL. Start and stop
conditions are recognized as the beginning and
end of a serial transfer.
3) Slave Address: Command/control byte is the first
byte received following the start condition from the
master device. The command/control byte con-
sists of a 4-bit control code. For the DS1857, this
is set as 1010 binary for read/write operations. The
next three bits of the command/control byte are
the device select bits or device address. They are
used by the master device to select which of eight
possible devices on the bus is to be accessed.
When reading or writing the DS1857, the device-
select bits must match one of two valid device
addresses 00h, or the address registered in
Table
01 location 8Ch. The last bit of the command/con-
trol byte (R/W) defines the operation to be per-
formed. When set to a ‘1’ a read operation is
selected, and when set to a ‘0’ a write operation is
selected. The slave address can be set by the
EEPROM.
Following the start condition, the DS1857 monitors the
SDA bus checking the device type identifier being
transmitted. Upon receiving the 1010 control code, the
appropriate device address bits, and the read/write bit,
the slave device outputs an acknowledge signal on the
SDA line.
Chip Topology
TRANSISTOR COUNT: 44149
SUBSTRATE CONNECTED TO GROUND.
STOP
CONDITION
OR REPEATED
START
CONDITION
REPEATED IF MORE BYTES
ARE TRANSFERRED
ACK
START
CONDITION
ACK
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
ACKNOWLEDGEMENT
SIGNAL FROM RECEIVER
SLAVE ADDRESS
MSB
SCL
SDA
R/W
DIRECTION
BIT
1 2 6 7 8 9 1 2 8 9 3–7
Figure 5. 2-Wire Data Transfer Protocol