1
Download CC253X User Guide
Transcript
Receive Mode www.ti.com There are three different sources for setting the pending bit in an ACK frame (i.e., the SACKPEND strobe, the PENDING_OR register bit, and the AUTOPEND feature). The pending bit is set if one or more of these sources are set. Transmission Timing Acknowledgment frames can only be transmitted immediately after frame reception. The transmission timing is controlled by the FSMCTRL.SLOTTED_ACK bit. 12 Symbol Periods = 192 ms Unslotted ACK (0) Preamble RX Frame SFD Preamble SFD ACK Frame Preamble SFD ACK Frame n Backoff Periods = n ´ 320 ms Slotted ACK (1) Preamble RX Frame SFD 12–31 Symbol Periods T0320-01 Figure 23-15. Acknowledgement Timing The IEEE 802.15.4 requires unslotted mode in nonbeacon-enabled PANs, and slotted mode for beacon-enabled PANs. Manual Control The SACK, SACKPEND, and SNACK command strobes can only be issued during frame reception. If the strobes are issued at any other time, they have no effect but generating a STROBE_ERROR interrupt. Preamble SFD STROBE_ ERROR RX Frame (Rejected or Accepted) STROBE_ ERROR Valid Strobe Interval T0321-01 Figure 23-16. Command Strobe Timing The command strobes may be issued several times during reception; however, only the last strobe has an effect: • No strobe / SNACK / incorrect FCS: No acknowledgment transmission • SACK: Acknowledgment transmission with the frame pending-bit cleared • SACKPEND: Acknowledgment transmission with the frame pending-bit set Automatic Control (AUTOACK) When FRMFILT0.FRM_FILTER_EN and FRMCTRL0.AUTOACK are both enabled, the radio determines automatically whether or not to transmit acknowledgment frames: • The RX frame must be accepted by frame filtering (indicated by the RX_FRM_ACCEPTED exception). • The acknowledgment request bit must be set in the RX frame. • The RX frame must not be a beacon or an acknowledgment frame. • The FCS of the RX frame must be correct. Automatic acknowledgments can be overridden by the SACK, SACKPEND, and SNACK command strobes. For instance, if the microcontroller is low on memory resources and cannot store a received frame, the SNACK strobe can be issued during reception and prevent acknowledging the discarded frame. By default, the AUTOACK feature never sets the frame-pending bit in the acknowledgment frames. Apart from manual override with command strobes, there are two options: • Automatic control, using the AUTOPEND feature • Manual control, using the FRMCTRL1.PENDING_OR bit 234 CC253x Radio SWRU191B – April 2009 – Revised September 2010 Submit Documentation Feedback Copyright © 2009–2010, Texas Instruments Incorporated
