CC2550-RTR1 datasheet(20/55 Pages) TI

20 / 55 page

CC2550

PRELIMINARY Data Sheet (Rev.1.2)

SWRS039A

Page 20 of 54

CC2550 supports both fixed packet length

protocols and variable packet length protocols.

Variable or fixed packet length mode can be

used for packets up to 255 bytes. For longer

packets, infinite packet length mode must be

used.

Fixed packet length mode is selected by

setting PKTCTRL0.LENGTH_CONFIG=0. The

desired packet length is set by the PKTLEN

variable

packet

length

mode,

PKTCTRL0.LENGTH_CONFIG=1,

the packet

length is configured by the first byte after the

sync word. The packet length is defined as the

payload data, excluding the length byte and

the optional automatic CRC.

With

PKTCTRL0.LENGTH_CONFIG

=2,

the

packet length is set to infinite and transmission

will continue until turned off manually. The

infinite mode can be turned off while a packet

is being transmitted. As described in the next

section, this can be used to support packet

formats with different length configuration than

natively supported by

CC2550.

13.2.1 Arbitrary length field configuration

By utilizing the infinite packet length option,

arbitrary packet length is available. At the start

of the packet, the infinite mode must be active.

On the TX side, the PKTLEN register is set to

mod(length,

256).

When less than 256

bytes remains of the packet the MCU disables

infinite packet length and activates fixed length

packets. When the internal byte counter

reaches the PKTLEN value, the transmission

ends. Automatic CRC appending/checking can

be used (by setting PKTCTRL0.CRC_EN to 1).

When for example a 600-byte packet is to be

transmitted, the MCU should do the following

(see also Figure 11):

•

Set PKTCTRL0.LENGTH_CONFIG=2 (10).

•

Pre-program the PKTLEN register to

mod(600,256)=88.

•

Transmit at least 345 bytes, for example

by filling the 64-byte TX FIFO six times

(384 bytes transmitted).

•

Set PKTCTRL0.LENGTH_CONFIG=0 (00).

•

The transmission ends when the packet

counter reaches 88. A total of 600 bytes

are transmitted.

Figure 11: Arbitrary length field configuration

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