DS1305
3-WIRE INTERFACE
The 3-wire interface mode operates similarly to the SPI mode. However, in 3-wire mode there is one I/O
instead of separate data in and data out signals. The 3-wire interface consists of the I/O (SDI and SDO
pins tied together), CE and SCLK pins. In 3-wire mode, each byte is shifted in LSB first unlike SPI mode
where each byte is shifted in MSB first.
As is the case with the SPI mode, an address byte is written to the device followed by a single data byte
or multiple data bytes. Figure 10 illustrates a read and write cycle. In 3-wire mode, data is input on the
rising edge of SCLK and output on the falling edge of SCLK.
3-WIRE SINGLE-BYTE TRANSFER Figure 10
Single Byte Read
RST
SCLK
I/O
A0 A1 A2 A3
A4 A5 A6 A7
Single Byte Write
RST
SCLK
I/O
A0 A1 A2 A3
A4 A5 A6 A7
D0
D1 D2 D3 D4 D5 D6 D7
In burst mode, RST is kept high and additional SCLK cycles are sent until the end of the burst.
* I/O is SDI and SDO tied together
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DALLAS [ DALLAS SEMICONDUCTOR ]
