SPIRIT1 datasheet(32/94 Pages) STMICROELECTRONICS

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Operating modes

SPIRIT1

32/94

Doc ID 022758 Rev 3

When setting TWU, care should be taken when considering the analog settling time which is

required before the radio becomes fully operative for transmission or reception (TIDLE in

Figure 5).

Figure 5.

LDCR mode timing

The TIDLE time can be longer than the minimum required to get analog circuits settling, and

this causes power waste. In order to minimize TIDLE, the SPIRIT1 supports the runtime

phasing of the internal wake-up timer, as follows:

●

The value of the wake-up timer can be reloaded during runtime using the

LDCR_RELOAD command with the values written in the

LDCR_RELOAD_PRESCALER/COUNTER registers. In doing so, the counting can be

delayed or anticipated

●

Alternatively, the wake-up timer can be automatically reloaded at the time the SYNC is

received. This option must be enabled on the PROTOCOL register and it is available

only for LDC mode in reception.

7.4

CSMA/CA engine

The CSMA/CA engine is a channel access mechanism based on the rule of sensing the

channel before transmitting. This avoids the simultaneous use of the channel by different

transmitters and increases the probability of correct reception of data being transmitted.

CSMA is an optional feature that can be enabled on the basis of user needs.

When CSMA is enabled, the device performs a clear channel assessment (CCA) before

transmitting any data. In SPIRIT1 implementation, CCA is based on a comparison of the

channel RSSI with a programmable static carrier sense threshold.

If the CCA finds the channel busy, a backoff procedure may be activated to repeat the CCA

process a certain number of times, until the channel is found to be idle. Each time that CCA

is retried, a counter (NB) is incremented by one, up to the upper limit (NBmax).

When the limit is reached, an NBACKOFF_MAX interrupt request is raised towards the

MCU, to notify that the channel has been repeatedly found busy and so the transmission

has not been performed.

While in backoff, the device stays in SLEEP/READY state in order to reduce power

consumption.

CCA may optionally be persistent, i.e., rather than entering backoff when the channel is

found busy, CCA continues until the channel becomes idle or until the MCU stops it.

The thinking behind using this option is to give the MCU the possibility of managing the CCA

by itself, for instance, with the allocation of a transmission timer: this timer would start when

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