CC2550-RTY1 datasheet(21/62 Pages) TI2

21 / 62 page

CC2550

SWRS039B

Page 21 of 58

sync word and then the data bytes. The

number of preamble bytes is programmed with

the MDMCFG1.NUM_PREAMBLE value.

The synchronization word is a two-byte value

set in the SYNC1 and SYNC0 registers. A one-

byte sync word can be emulated by setting the

SYNC1

value to the preamble pattern. It is also

possible to emulate a 32 bit sync word by

using MDMCFG2.SYNC_MODE=3 or 7. The sync

word will then be repeated twice.

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. As

described in the next section, this can be used

to support packet formats with different length

configuration than natively supported by

CC2550. One should make sure that TX mode

is not turned off during the transmission of the

first half of any byte. Refer to the

CC2550

Errata Notes [1] for more details.

Note

that

the

minimum

packet

length

supported (excluding the optional length byte

and CRC) is one byte of payload data.

13.2.1 Packet Length > 255

Reprogramming the packet automation control

the possibility to transmit packets that are

longer than 256 bytes and still be able to use

the packet handling hardware support. At the

start of the packet, the infinite packet length

mode (PCKCTRL0.LENGTH_CONFIG=2) must

be active. The PKTLEN register is set to

mod(length, 256). When less than 256 bytes

remains of the packet the MCU disables

infinite packet length mode and activates fixed

packet length mode. When the internal byte

counter reaches the PKTLEN

value, the

transmission ends the radio enters the state

determined by TXOFF_MODE). Automatic CRC

appending

can

used

(by

setting

PKTCTRL0.CRC_EN

=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.

•

Pre-program the PKTLEN register to

mod(600,256)=88.

•

Transmit at least 345 bytes (600 – 255),

for example by filling the 64-byte TX FIFO

six times (384 bytes transmitted).

•

Set PKTCTRL0.LENGTH_CONFIG=0.

•

The transmission ends when the packet

counter reaches 88. A total of 600 bytes

are transmitted.

Figure 11: Packet Length > 255

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