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Data Input
(LSB First)
r0
r1
r2
r3
r4
r5
r6
r7
r8
r9
r10
r11
r12
r13
r14
r15
B0307-01
Receive Mode
Figure 23-9. FCS Hardware Implementation
23.8.11 Interrupts
The SFD interrupt is raised when the SFD field of the frame has been transmitted. At the end of the frame,
the TX_FRM_DONE interrupt is raised when the complete frame has been successfully transmitted.
Note that there is a second SFD signal available on GPIO (through radio observation mux) that should not
be confused with the SFD interrupt.
23.8.12 Clear-Channel Assessment
The clear-channel assessment (CCA) status signal indicates whether the channel is available for
transmission or not. The CCA function is used to implement the CSMA-CA functionality specified in the
IEEE 802.15.4 specification [1]. The CCA signal is valid when the receiver has been enabled for at least
eight symbol periods. The
RSSI_VALID
status signal can be used to verify this.
The CCA is based on the RSSI value and a programmable threshold. The exact behavior is configurable
in the
CCACTRL0
and
CCACTRL1
registers.
There are two variations of the CCA signal, one that is updated at every new RSSI sample and one that is
only updated on SSAMPLECCA/ISAMPLECCA and STXONCCA/ISTXONCCA command strobes. They
are both available in the
FSMSTAT1
register.
Note that the CCA signal is updated four clock cycles (system clock) after the
RSSI_VALID
signal has
been set.
23.8.13 Output Power Programming
The RF output power is controlled by the 7-bit value in the
TXPOWER
register. The device data sheet
(
) shows typical output power and current consumption for recommended settings when the
center frequency is set to 2.440 GHz. Note that the recommended settings are only a small subset of all
the possible register settings.
23.8.14 Tips and Tricks
•
Note that there is no requirement to have the complete frame in the TXFIFO before starting a
transmission. Bytes may be added to the TXFIFO during transmission.
•
It is possible to transmit non-IEEE 802.15.4 compliant frames by setting
MDMTEST1.MODULATION_MODE
= 1.
23.9 Receive Mode
This section describes how to control the receiver, control the integrated RX frame processing, and how to
use the RXFIFO.
23.9.1 RX Control
The receiver is turned on and off with the SRXON and SRFOFF command strobes, and with the
RXENABLE
registers. The command strobes provide a hard on/off mechanism, whereas
RXENABLE
manipulation provides a soft on/off mechanism.
The receiver is turned on by the following actions:
•
The SRXON strobe:
233
SWRU191C
–
April 2009
–
Revised January 2012
CC253x Radio
Copyright
©
2009
–
2012, Texas Instruments Incorporated