SI4455-C2A-GMR Datasheet, PDF (23/39 Pages) Silicon Laboratories – EASY-TO-USE, LOW-CURRENT OOK/(G)FSK SUB-GHZ TRANSCEIVER, TRANSMITTER, AND RECEIVER

Si4x55-C
The Si4x55 contains an internal MCU which controls all the internal functions of the radio. For SPI read commands,
a typical communication 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 11 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 12 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.
Send Command
Read CTS
0xFF
CTS Value
0x00
Retrieve
Response
nSEL
SDO
CTS
SDI
ReadCmdBuff
SCLK
Figure 11. SPI Read Command—Check CTS Value
nSEL
SDO
SDI
SCLK
Response Byte 0
Response Byte n
Figure 12. SPI Read Command—Clock Out Read Data
Rev 1.0
23