SI4420 Datasheet, PDF (11/33 Pages) Silicon Laboratories – No alignment required in production

Si4420
CONTROL INTERFACE
Commands (or TX data) to the transceiver are sent serially. Data bits on pin SDI are shifted into the device upon the rising edge of the clock
on pin SCK whenever the chip select pin nSEL is low. When the nSEL signal is high, it initializes the serial interface. All commands consist of
a command code, followed by a varying number of parameter or data bits. All data are sent MSB first (e.g. bit 15 for a 16-bit command). Bits
having no influence (don’t care) are indicated with X. The Power On Reset (POR) circuit sets default values in all control and command
registers.
The status information or received data can be read serially over the SDO pin. Bits are shifted out upon the falling edge of CLK signal. When
the nSEL is high, the SDO output is in a high impedance state.
The receiver will generate an interrupt request (IT) for the microcontroller - by pulling the nIRQ pin low - on the following events:
 The TX register is ready to receive the next byte (RGIT)
 The FIFO has received the preprogrammed amount of bits (FFIT)
 Power-on reset (POR)
 FIFO overflow (FFOV) / TX register underrun (RGUR)
 Wake-up timer timeout (WKUP)
 Negative pulse on the interrupt input pin nINT (EXT)
 Supply voltage below the preprogrammed value is detected (LBD)
FFIT and FFOV are applicable when the FIFO is enabled. RGIT and RGUR are applicable only when the TX register is enabled. To identify the
source of the IT, the status bits should be read out.
Timing Specification
Symbol
tCH
tCL
tSS
tSH
tSHI
tDS
tDH
tOD
Parameter
Clock high time
Clock low time
Select setup time (nSEL falling edge to SCK rising edge)
Select hold time (SCK falling edge to nSEL rising edge)
Select high time
Data setup time (SDI transition to SCK rising edge)
Data hold time (SCK rising edge to SDI transition)
Data delay time
Timing Diagram
Minimum value [ns]
25
25
10
10
25
5
5
10
nSEL
SCK
SDI
t_SS
t_CH
t_CL
t_DS
t_DH
BIT15
BIT14
BIT13
t_OD
BIT8
BIT7
t_SHI
t_SH
BIT1
BIT0
SDO
FFIT
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