SPIRIT1 datasheet(55/94 Pages) STMICROELECTRONICS

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SPIRIT1

Transmission and reception

Doc ID 022758 Rev 3

55/94

Preamble (programmable field): the length of the preamble is programmable from 1 to 32

bytes by the PREAMBLE_LENGTH field of the PCKTCTRL2 register. Each preamble byte is

a '10101010' binary sequence.

Sync (programmable field): the length of the synchronization field is programmable (from 1

to 4 bytes) through dedicated registers. The synchronization word is programmable through

registers SYNC1, SYNC2, SYNC3, and SYNC4. If the programmed sync length is 1 then

only the SYNC1 word is transmitted; if the programmed sync length is 2 then only SYNC1

and SYNC2 words are transmitted and so on.

Length (programmable/optional field): the packet length field is an optional field that is

defined as the cumulative length of Address (2 bytes always), Control, and Payload fields. It

is possible to support fixed and variable packet length. In fixed mode, the field length is not

used.

Destination address (programmable field): When the destination address filtering is

enabled in the receiver, the packet handler engine compares the destination address field of

the packet received with the value of register TX_SOURCE_ADDR. If broadcast address

and/or multicast address filtering are enabled the packet handler engine compares the

destination address with the programmed broadcast and/or multicast address.

Source address (programmable field): is filled with the value of register

TX_SOURCE_ADDR. When source address filtering is enabled in the receiver, the packet

handler engine compares the source address received with the programmed source

address reference using the source mask address programmed.

The field ADDRESS_LEN of the PCKTCTRL4 register must be set always to 2.

Control (programmable/optional field): is programmable from 0 to 4 bytes through the

CONTROL_LEN field of the PCKTCTRL4 register. Control fields of the packet can be set

using the TX_CTRL_FIELD[3:0] register.

Sequence number (programmable field): is a 2-bit field and contains the sequence number

of the transmitted packet. It is incremented automatically every time a new packet is

transmitted. In the receiver it is used (together with the CRC field) to detect if the received

packet is new or retransmitted. It can be re-loaded with the value in the

TX_SEQ_NUM_RELOAD[1:0] field of the PROTOCOL[2] register, by using the

SEQUENCE_UPDATE command.

NO_ACK (programmable field): 1 means for the receiver that the packet is not to be auto-

acknowledged. It is programmed by the bit field NACK_TX of the register PROTOCOL[2]. It

is important set to 0 this bit field in any other packet format.

Payload (programmable/optional field): the device supports both fixed and variable payload

length transmission from 0 to 65535 bytes.

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

On the receiver, if the field FIX_VAR_LEN of the 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.

In variable length mode, the width of the binary field transmitted, where the actual length of

payload is written, can be configured through the field LEN_WIDTH of the PCKTCTRL3

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