Rainbow Electronics DS1305 - Manual (Page 12)

DS1305
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Figure 5. SERIAL CLOCK AS A FUNCTION OF MICROCONTROLLER CLOCK
POLARITY (CPOL)
1) CPHA bit polarity (if applicable) may need to be set accordingly.
2) CPOL is a bit that is set in the microcontroller’s control register.
3) SDO remains at high-Z until 8 bits of data are ready to be shifted out during a read.
ADDRESS AND DATA BYTES
Address and data bytes are shifted MSB first into the serial data input (SDI) and out of the serial data
output (SDO). Any transfer requires the address of the byte to specify a write or read to either a RTC or
RAM location, followed by one or more bytes of data. Data is transferred out of the SDO for a read
operation and into the SDI for a write operation (Figures 6 and 7).
Figure 6. SPI SINGLE-BYTE WRITE
Figure 7. SPI SINGLE-BYTE READ
*SCLK can be either polarity.
CE
CPOL = 1
SCLK
DATA LATCH (WRITE)
SHIFT DATA OUT (READ)
CPOL = 0
SCLK
DATA LATCH (WRITE)
SHIFT DATA OUT (READ)