SPIRIT1 datasheet(58/94 Pages) STMICROELECTRONICS

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Transmission and reception

SPIRIT1

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Doc ID 022758 Rev 3

On the transmitter, the payload length is always set as: PCKTLEN1 × 256 + PCKTLEN0.

On the receiver, if the field FIX_VAR_LEN of PCKTCTRL2 register is set to 1, the payload

length is directly extracted from the received packet itself; if FIX_VAR_LEN is set to 0, the

payload length is controlled by the PCKTLEN0 and PCKTLEN1 registers as the transmitter.

Furthermore, in variable length mode, the width of the binary field transmitted, where the

actual length of payload is written, must be configured through the field LEN_WIDTH of the

PCKTCTRL3 register according to the maximum length expected in the specific application.

Example 1

●

If the variable payload length is from 0 to 31 bytes, then LEN_WIDTH = 5

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If the variable payload length is from 0 to 255 bytes, then LEN_WIDTH = 8

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If the variable payload length is from 0 to 65535 bytes, then LEN_WIDTH = 16.

CRC (programmable/optional field): There are different polynomials CRC: 8 bits, 16 bits (2

polynomials are available) and 24 bits. When the CRC automatic filtering is enabled, the

received packet is discarded automatically when the CRC check fails.

9.7.4

Automatic packet filtering

The following filtering criteria to automatically reject a received packet are supported:

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CRC filtering

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Destination address filtering

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Source address filtering

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Control field filtering.

Packet filtering is enabled by the AUTO_PCKT_FLT field of the PROTOCOL register and the

filtering criteria can be controlled by the PCK_FLT_OPT and PCK_FLT_GOALS registers.

Each filtering option works on the correct packet format according to Table 30.

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CRC: the received packet is discarded if CRC is not passed. To enable this automatic

filtering feature the bit field CRC_CHECK of the PCK_FLT_OPT register must be set.

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Destination address: this automatic filtering feature works on my address, broadcast

address and/or multicast address of the receiver.

–

Destination vs. my address: the received packet is discarded if the destination

address received does not match the programmed my address of the receiver. My

address can be programmed for the receiver in the TX_SOURCE_ADDR register.

To enable this automatic filtering option the bitfield DEST_VS_SOURCE_ADDR of

the PCKT_FLT_OPTIONS register must be set.

–

Destination vs. broadcast address: the received packet is discarded if the

destination address received does not match the programmed broadcast address

of the receiver. The broadcast address can be programmed for the receiver in the

BROADCAST register. To enable this automatic filtering option the bitfield

DEST_VS_BROADCAST_ADDR of the PCKT_FLT_OPTIONS register must be

set.

–

Destination vs. multicast address: the received packet is discarded if the

destination address received does not match the programmed multicast address

of the receiver. The multicast address can be programmed for the receiver in the

MULTICAST register. To enable this automatic filtering option the bitfield

DEST_VS_MULTICAST_ADDR of the PCKT_FLT_OPTIONS register must be

set.

SPIRIT1 Datasheet(PDF) 58 Page - STMicroelectronics

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