Rainbow Electronics RF12B - Manual (Page 12)

RF12B
CONTROL INTERFACE
Commands to the transmitter 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 receiver will generate an interrupt request (IT) for the microcontroller - by pulling the nIRQ pin
low - on the following events:
z The TX register is ready to receive the next byte (RGIT)
z The FIFO has received the preprogrammed amount of bits (FFIT)
z Power-on reset (POR)
z FIFO overflow (FFOV) / TX register underrun (RGUR)
z Wake-up timer timeout (WKUP)
z Negative pulse on the interrupt input pin nINT (EXT)
z 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 Parameter Minimum value [ns]
t
C H
Clock high time 25
t
C L
Clock low time 25
t
S S
Select setup time (nSEL falling edge to SCK rising edge) 10
t
S H
Select hold time (SCK falling edge to nSEL rising edge) 10
t
S H I
Select high time 25
t
D S
Data setup time (SDI transition to SCK rising edge) 5
t
D H
Data hold time (SCK rising edge to SDI transition) 5
t
O D
Data delay time 10
Timing Diagram
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