Bluetooth LE/IEEE 802.15.4 timing

3-wire with multiplexed priority

The following diagram shows external Bluetooth LE/IEEE 802.15.4 timing parameters when SR_STATUS carries both priority and TX/RX information in a time multiplexed manner.

Figure 1. 3-wire timing with priority multiplexing

Table 1. Bluetooth LE/IEEE 802.15.4 timing parameters
Parameter	Description
T1: SR_REQUEST lead time period	The time SR_REQUEST is asserted before actual transactions.
T2: SR_STATUS	The time when SR_STATUS is sampled to get SR_PTI information.
T3: SR_GRANT	The time before PTA should post SR_GRANT so that it is stable to be considered by the Bluetooth LE/IEEE 802.15.4 device.

The Bluetooth LE/IEEE 802.15.4 timing parameters are used to derive Packet Traffic Arbitration (PTA) timing parameters. The following table describes the relationship between PTA timing parameters and Bluetooth LE/IEEE 802.15.4 timing parameters.

Table 2. PTA and Bluetooth LE/IEEE 802.15.4 timing parameters
PTA timing parameter	Relation with Bluetooth LE/IEEE 802.15.4 timing parameter
Bluetooth LE/IEEE 802.15.4 device status priority sampling time (t2)	t1 < t2 < (t1+T2)
PTA arbitration decision time (t3)	(t1+T2) < t3 < (T1-T3)

Table 3. Time instances
Time instance	Description
t1	The time instance when SR_REQUEST is asserted.
t2	The time instance when SR_STATUS is sampled to get SR_PTI information. This can be any time during T2.
t3	The time instance when PTA takes an arbitration decision and posts SR_GRANT to the Bluetooth LE/IEEE 802.15.4 device. This is chosen a couple of microseconds before the start of the SR grant lead time period. This ensures that SR_GRANT is asserted as close to SR grant lead time period and is stable by the time the Bluetooth LE/IEEE 802.15.4 device uses this information to continue or abort the transaction.
t4	The time instance when the SR grant lead time period starts. This is the time when SR_GRANT must be stable to be considered by the Bluetooth LE/IEEE 802.15.4 device.
t5	The time instance when the actual transaction of the Bluetooth LE/IEEE 802.15.4 device starts. This is the time when the signaling period ends and the transaction period starts. Bluetooth LE/IEEE 802.15.4 Tx and Rx information is provided by changing the SR_STATUS signal level appropriately. PTA should track SR_STATUS if SR_REQUEST is high and update the information SR_TX_RX.

3-wire without multiplexed priority

If SR_STATUS carries only one parameter information (3-wire, no priority mode), then the default information that it carries is SR_TX_RX. In this case, SR_STATUS is set to TX or RX when SR_REQUEST is HIGH. The following diagram shows SR_STATUS only carrying TX/RX information. The signals are represented as a bus even though they are single bit ports to indicate transitions happening on the ports.

Figure 2. 3-wire timing without priority multiplexing

During the transaction, the Bluetooth LE/IEEE 802.15.4 device changes SR_STATUS appropriately to indicate TX and RX information. PTA continuously tracks SR_STATUS while SR_REQUEST is high and updates SR_TX_RX status internally for corresponding COEX behavior.

4-wire timing

In the following diagram, Bluetooth LE/IEEE 802.15.4 priority is explicitly signaled on the BT_COEX_STATUS1 pin.