CC2500_06 Datasheet, PDF(28/84 Page) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

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CC2500_06 Datasheet, PDF (28/84 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transceiver

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CC2500

Fixed packet length mode is selected by

setting PKTCTRL0.LENGTH_CONFIG=0. The

desired packet length is set by the PKTLEN

In 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. The PKTLEN

length allowed in RX. Any packet received with

a length byte with a value greater than

PKTLEN will be discarded.

With PKTCTRL0.LENGTH_CONFIG=2, the

packet length is set to infinite and transmission

and reception will continue until turned off

manually. The infinite mode can be turned off

while a packet is being transmitted or received.

As described in the next section, this can be

used to support packet formats with different

length configuration than natively supported by

CC2500.

15.2.1 Arbitrary Length Field Configuration

The fixed length field can be reprogrammed

during receive and transmit. This opens the

possibility to have a different length field

configuration than supported for variable

length packets. At the start of reception, the

packet length is set to a large value. The MCU

reads out enough bytes to interpret the length

field in the packet. Then the PKTLEN value is

set according to this value. The end of packet

will occur when the byte counter in the packet

handler is equal to the PKTLEN register. Thus,

the MCU must be able to program the correct

length, before the internal counter reaches the

packet length.

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). On the RX side the

MCU reads out enough bytes to interpret the

length field in the packet and sets the PKTLEN

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 or reception 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 12):

â¢ Set PKTCTRL0.LENGTH_CONFIG=2 (10).

â¢ Pre-program the PKTLEN register to

mod(600,256)=88.

â¢ Transmit at least 345 bytes, for example

by filling the 64-byte TX FIFO six times

(384 bytes transmitted).

â¢ Set PKTCTRL0.LENGTH_CONFIG=0 (00).

â¢ The transmission ends when the packet

counter reaches 88. A total of 600 bytes

are transmitted.

Internal byte counter in packet handler counts from 0 to 255 and then starts at 0 again

0,1,.......... ,88,.................... 255,0,........,88,.................. ,255,0,........,88,.................. ,255,0,.......................

Infinite packet length enabled

Fixed packet length

enabled when less than

256 bytes remains of

packet

600 bytes transmitted and

received

Length field transmitted and received. Rx and Tx PKTLEN value set to mod(600,256) = 88

Figure 12: Arbitrary length field configuration

PRELIMINARY Data Sheet (Rev.1.2) SWRS040A

Page 28 of 83

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