Texas Instruments 3138 155 232931 manual Acknowledge frame format

CC2420

AUTOACK may be used for non-beacon systems as long as the frame pending field (see Figure 19) is cleared. The acknowledge frame is then transmitted 12

symbol periods after the last symbol of the incoming frame. This is as specified by [1] for non-beacon networks.

Bytes:	4	1	1	2	1	2
	Preamble	Start of Frame	Frame	Frame	Data	Frame Check
		Delimiter		Control Field	Sequence	Sequence
	Sequence		Length
		(SFD)		(FCF)	Number	(FCS)
	Synchronisation	Header	PHY Header	MAC Header	(MHR)	MAC Footer
	(SHR)		(PHR)			(MFR)

Figure 23. Acknowledge frame format [1]

Two command strobes, SACK and SACKPEND are defined to transmit acknowledge frames with the frame pending field cleared or set, respectively. The acknowledge frame is only transmitted if the CRC is valid.

For systems using beacons, there is an additional timing requirement that the acknowledge frame transmission should be started on the first backoff-slot boundary (20 symbol periods) at least 12 symbol periods after the last symbol of the incoming frame. This timing must be controlled by the microcontroller by issuing the SACK and SACKPEND command strobe 12 symbol periods before the following backoff-slot boundary, as illustrated in Figure 24.

If a SACK or SACKPEND command strobe is issued while receiving an incoming frame, the acknowledge frame is transmitted 12 symbol periods after the last symbol of the incoming frame. This should be used to transmit acknowledge frames in non-beacon networks. This timing is also illustrated in Figure 24.

Using SACKPEND will set the pending data flag for automatically transmitted acknowledge frames using AUTOACK. The pending flag will then be set also for future acknowledge frames, until a SACK command strobe is issued.

Acknowledge frames may be manually

transmitted using normal data transmission if desired.

Beacon network

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Figure 24. Acknowledge frame timing

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