SI4464 Datasheet, PDF (17/56 Pages) Silicon Laboratories – HIGH-PERFORMANCE

Si4464/63/61/60
3. Controller Interface
3.1. Serial Peripheral Interface (SPI)
The Si446x communicates with the host MCU over a standard 4-wire serial peripheral interface (SPI): SCLK, SDI,
SDO, and nSEL. The SPI interface is designed to operate at a maximum of 10 MHz. The SPI timing parameters
are demonstrated in Table 8. The host MCU writes data over the SDI pin and can read data from the device on the
SDO output pin. Figure 3 demonstrates an SPI write command. The nSEL pin should go low to initiate the SPI
command. The first byte of SDI data will be one of the firmware commands followed by n bytes of parameter data
which will be variable depending on the specific command. The rising edges of SCLK should be aligned with the
center of the SDI data.
Table 8. Serial Interface Timing Parameters
Symbol
t_CH
t_CL
t_DS
t_DH
t_DD
t_EN
t_DE
t_SS
t_SH
t_SW
Parameter
Clock high time
Clock low time
Data setup time
Data hold time
Output data delay time
Output enable time
Output disable time
Select setup time
Select hold time
Select high period
Min (ns)
40
40
20
SCLK
tSS
20
20
SDI
20
50
SDO
20
tEN
50
nSEL
80
Diagram
tCL
tCH
tDS tDH
tDD
tSH tDE
tSW
nSEL
SDO
SDI
FW Command
Param Byte 0
Param Byte n
SCLK
Figure 3. SPI Write Command
The Si446x contains an internal MCU which controls all the internal functions of the radio. For SPI read commands
a typical MCU flow of checking clear-to-send (CTS) is used to make sure the internal MCU has executed the
command and prepared the data to be output over the SDO pin. Figure 4 demonstrates the general flow of an SPI
read command. Once the CTS value reads FFh then the read data is ready to be clocked out to the host MCU. The
typical time for a valid FFh CTS reading is 20 µs. Figure 5 demonstrates the remaining read cycle after CTS is set
to FFh. The internal MCU will clock out the SDO data on the negative edge so the host MCU should process the
SDO data on the rising edge of SCLK.
Rev 1.2
17