A N 6 9 2
14
Rev 0.4
4.2.2. Checking that the Radio is Ready to Receive Commands
4.2.2.1. Software Polling Method
To ensure the radio is ready to receive the next command, the host MCU must pull down the NSEL pin to monitor
the status of CTS over the SPI port. The 0x44 command ID has to be sent, and eight clock pulses have to be
generated, on the SCLK pin. During the additional eight clock cycles, the radio clocks out the CTS as a byte on the
SDO pin. When completed, the NSEL should be pulled back to high. If the CTS byte is 0xFF, then the radio
processed the last command successfully and is ready to receive the next command; in any other case, the CTS
read procedure has to be repeated from the beginning as long as the CTS byte is not 0xFF.
Figure 8. Polling the Radio Availability
4.2.2.2. GPIO Checking Method
Any GPIO can be configured for monitoring the CTS. GPIOs can be configured to go either high or low when the
chip completes the command. The function of the GPIOs can be changed by the
GPIO_PIN_CFG
command. By
default, GPIO1 is set as “High when command completed, low otherwise” after Power On Reset. Therefore, this pin
can be used for monitoring the CTS right after Power On Reset and to identify when the chip is ready to boot up.
4.2.2.3. NIRQ Interrupt Checking Method
The radio asserts the CHIP_READY interrupt flag if a command is completed. The interrupt flag can be monitored
by either the GET_CHIP_STATUS or the GET_INT_STATUS command. Apart from monitoring the interrupt flags,
the radio may pull down the NIRQ pin if this feature is enabled. If a new command is sent while the CTS is
asserted, then the radio ignores the new command. The Si446x can generate an interrupt to communicate this
error to the MCU by the CMD_ERROR interrupt flag in the CHIP_STATUS group. The interrupt flag has to be read
(by issuing a GET_CHIP_STATUS or GET_INTERRUPT_STATUS command) to clear the pending interrupt and
release the NIRQ pin. No other action is needed to reset the command buffer of the radio; however, after a
CMD_ERROR, the host MCU should repeat the new command after the radio has processed the previous one.
All the commands that are sent to the radio have the same structure. After pulling down the NSEL pin of the radio,
the command ID should be sent first. The commands may have up to 15 input parameters.
Figure 9. Host MCU Sends Command to Radio
Summary of Contents for Si4455 Series
Page 8: ...AN692 8 Rev 0 4 Figure 6 Device Configuration Options ...
Page 22: ...AN692 22 Rev 0 4 Figure 21 Supply Current versus Time Diagram from Shutdown to RX State ...
Page 23: ...AN692 Rev 0 4 23 4 4 Radio Chip Waking Up Figure 22 Radio Wake Up Process ...
Page 35: ...AN692 Rev 0 4 35 Figure 32 Transmission Flowchart ...
Page 39: ...AN692 Rev 0 4 39 Figure 33 Reception Flowchart ...
Page 41: ...AN692 Rev 0 4 41 Figure 34 Bidirectional Variable Packet Example Project Flowchart ...
Page 47: ...AN692 Rev 0 4 47 Figure 41 Long Packet Transmission Flowchart ...
Page 48: ...AN692 48 Rev 0 4 Figure 42 Long Packet RX Flowchart ...
