STW81103 Datasheet, PDF (36/53 Pages) STMicroelectronics – Multi-band RF frequency synthesizer with integrated VCOs

SPI digital interface
7
SPI digital interface
STW81103
7.1
General features
The SPI digital interface is selected by hardware connection of pin #21 (DBUS_SEL) to
3.3 V.
The STW81103 IC is programmed by means of a high-speed serial-to-parallel interface with
write option only. The 3-wire bus can be clocked at a frequency as high as 100 MHz to allow
fast programming of the registers containing the data for RF IC configuration.
The chip is programmed through serial words with a full length of 26 bits. The first 2 MSBs
represent the address of the registers, and the 24 LSBs represent the value of the registers.
Each data bit is stored in the internal shift register on the rising edge of the CLOCK signal.
The outputs of the selected register are sent to the device on the rising edge of the LOAD
signal.
Figure 26. SPI input and output bit order
Last bit sent
(LSB)0
DATA
2
1
23 25(MSB)
24
A1
LOAD
Address
decoder
D23 (MSB)
LOAD #4
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D0 (LSB)
Reg.#0
Reg.#1
Reg.#4