Texas Instruments 3138 155 232931 manual Pin activity examples during receive

Data received over RF

Address	SFD Pin
recognition OK
	FIFO Pin

FIFOP Pin, if threshold higher than frame length

FIFOP Pin, if threshold lower than frame length

Data received over RF

Address	SFD Pin
recognition fails
	FIFO Pin
	FIFOP Pin

CC2420

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SFD

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MAC Protocol Data Unit (MPDU) with correct address

Preamble SFD Length MAC Protocol Data Unit (MPDU) with wrong address

Figure 13. Pin activity examples during receive

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SFD
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SI	ADDRTXFIFO	-	-	-	-	-	-	-	-	-
SO	Status	Length	PSDU0	PSDU1	PSDU2	PSDU3	PSDU4	PSDU5	RSSI	FCS/Corr

FIFOP

FIFO

Figure 14. Example of pin activity when reading RXFIFO.

14.4 Transmit mode

During transmit the FIFO and FIFOP pins are still only related to the RXFIFO. The SFD pin is however active during transmission of a data frame, as shown in Figure 15.

The SFD pin goes active when the SFD field has been completely transmitted. It goes inactive again when the complete MPDU (as defined by the length field) has been transmitted or if an underflow is

detected. See the RF Data Buffering section on page 39 for more information on TXFIFO underflow.

As can be seen from comparing Figure 13 and Figure 15, the SFD pin behaves very similarly during reception and transmission of a data frame. If the SFD pins of the transmitter and the receiver are compared during the transmission of a data frame, a small delay of approximately 2 µs can be seen because of bandwidth limitations in both the transmitter and the receiver.

SWRS041B Page 34 of 89