Texas Instruments CC253x User Manual

Slotted ACK (1)
SFD
Unslotted ACK (0)
RX Frame
SFD ACK Frame
Preamble
SFD
RX Frame
SFD ACK Frame
Preamble
Preamble
Preamble
12SymbolPeriods=192 sm
12–31SymbolPeriods
nBackoffPeriods=n 320 s´ m
T0320-01
SFD
Preamble
Valid Strobe Interval
STROBE_ ERROR
STROBE_ ERROR
RXFrame(Rejectedor Accepted)
T0321-01
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.
Figure 23-17. Acknowledgment 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.
Figure 23-18. 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
242
CC253x Radio SWRU191C–April 2009–Revised January 2012
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Texas Instruments CC253x Specifications

General

Brand	Texas Instruments
Model	CC253x
Category	Microcontrollers
Language	English