Silicon Laboratories SI4421 manual Si4421, Status Read Command, Bit Name

Si4421

17. Status Read Command

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0	POR
	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0000h

The read command starts with a zero, whereas all other control commands start with a one. If a read command is identified, the status bits will be clocked out on the SDO pin as follows:

Status Register Read Sequence with FIFO Read Example:

Bit Name Function

RGIT	TX register is ready to receive the next byte (Can be cleared by Transmitter Register Write Command, page 24)
FFIT	The number of data bits in the RX FIFO has reached the pre-programmed limit (Can be cleared by any of the
	FIFO read methods)
POR	Power-on reset (Cleared after Status Read Command)
RGUR	TX register under run, register over write (Cleared after Status Read Command)
FFOV	RX FIFO overflow (Cleared after Status Read Command)
WKUP	Wake-up timer overflow (Cleared after Status Read Command)
EXT	Logic level on interrupt pin (pin 16) changed to low (Cleared after Status Read Command)
LBD	Low battery detect, the power supply voltage is below the pre-programmed limit
FFEM	FIFO is empty
ATS	Antenna tuning circuit detected strong enough RF signal
RSSI	The strength of the incoming signal is above the pre-programmed limit
DQD	Data quality detector output
CRL	Clock recovery locked
ATGL	Toggling in each AFC cycle
OFFS(6)	MSB of the measured frequency offset (sign of the offset value)
OFFS(3) -OFFS(0)	Offset value to be added to the value of the frequency control parameter (Four LSB bits)

Note: In order to get accurate values the AFC has to be disabled during the read by clearing the en bit in the AFC Control Command (page 21). The AFC offset value (OFFS bits in the status word) is represented as a two’s complement number. The actual frequency offset can be calculated as the AFC offset value multiplied by the current PLL frequency step (see the Frequency Setting Command on page 17).

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