TH7122 Datasheet, PDF (19/44 Pages) Melexis Microelectronic Systems – 27 to 930MHz FSK/FM/ASK Transceiver

4.1.3 Modulation Type
Modulation type
ASK / FSK
TH7122
27 to 930MHz
FSK/FM/ASK Transceiver
ASK
0
FSK
1
4.1.4 LNA Gain Mode
LNA gain
high
low
GAIN_LNA
0
1
4.2 Programmable User Mode Operation
The transceiver can also be used in programmable user mode. After power-up the first logic change at pin
FS0/SDEN enters into this mode. Now full programmability can be achieved via the Serial Control Interface
(SCI).
4.2.1 Serial Control Interface Description
A 3-wire (SCLK, SDTA, SDEN) Serial Control Interface (SCI) is used to program the transceiver in program-
mable user mode. At each rising edge of the SCLK signal, the logic value on the SDTA pin is written into a
24-bit shift register. The data stored in the shift register are loaded into one of the 4 appropriate latches on
the rising edge of SDEN. The control words are 24 bits lengths: 2 address bits and 22 data bits. The first two
bits (bit 23 and 22) are latch address bits. As additional leading bits are ignored, only the least significant 24
bits are serial-clocked into the shift register. The first incoming bit is the most significant bit (MSB). To
program the transceiver in multi-channel application, four 24-bit words may be sent: A-word, B-word, C-word
and D-word. If individual bits within a word have to be changed, then it is sufficient to program only the
appropriate 24-bit word. The serial data input timing and the structure of the control words are illustrated in
Fig. 12 and 13.
SDTA
SCLK
SDEN
22
24-BIT
SHIFT REGISTER
2
‘00’
‘01’
ADDR DECODER ‘10’
‘11’
22
A - LATCH ²²
A-word
22
B - LATCH ²²
B-word
22
C - LATCH ²²
C-word
22
D - LATCH ²²
D-word
Fig. 12: SCI Block Diagram
39010 07122
Rev. 008
Page 19 of 44
Data Sheet
June/07