SPIRIT1 datasheet(31/94 Pages) STMICROELECTRONICS

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SPIRIT1

Operating modes

Doc ID 022758 Rev 3

31/94

Note:

An SRES command is also available which generates an internal RESET of the SPIRIT1.

7.2

Timer usage

Most of the timers are programmable via R/W registers. All timer registers are made up of

two bytes: the first byte is a multiplier factor (prescaler); the second byte is a counter value.

Note:

If the counter register value (prescaler register value) is 0, the related timer never stops

(infinite timeout), despite the value written in the prescaler register (counter register).

The available timers and their features are listed in the following table.

Note:

For LDCR_COUNTER and LDCR_PRESCALER only, the effective number of cycles

counted is given by the value + 1 (e.g. counter=1 and prescaler=1 produces 2 x 2=4 counts,

counter=1 and prescaler=2 produces 2 x 3=6 counts, etc.).

The max period of RX TIMEOUT is related to an XO of 26 MHz.

7.3

Low duty cycle reception mode

The SPIRIT1 provides an operating mode, low duty cycle reception (LDCR), which is an

operating mode that allows operation with very low power consumption, while at the same

time keeping an efficient communication link. The LDCR mode is enabled by setting the

LDCR_MODE bit in the PROTOCOL registers.

This mode is available for both the transmitter and receiver and it is designed to allow for at

most one sequence RX+TX or TX+RX.

The device provides a set of timers to efficiently handle low duty cycle reception (LDCR).

When LDCR is enabled the device runs on the 34.7 kHz RC oscillator keeping unused

blocks off.

LDCR is controlled essentially by the wake-up period (TWU), which periodically wakes up

the SPIRIT1 to perform a transmission or a reception.

In reception mode, it is also relevant to set up the RX timeout in order to minimize the

amount of time the SPIRIT1 waits for a packet during TWU.

Timer period= PRESCALER x CONTER x Tclk

Table 20.

SPIRIT1 timers description and duration

No.

Description

Source

Time

step

Max. time

RX_TIMEOUT_PRESCALER

RX operation timeout

XO/1210

~46µs

~3s

RX_TIMEOUT_COUNTER

LDCR_PRESCALER

Wake-up period

RCO

~29µs

~2s

LDCR_COUNTER

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