Frequency And Channel Programming; Modulation Formats; Receiver; Supported Modulation Formats, Data Rates, And Deviations - Texas Instruments CC253x User Manual

Frequency and Channel Programming

25.5 Frequency and Channel Programming
For normal transmit and receive tasks, the carrier frequency is set by using the PRF_CHAN.FREQ register.
The carrier frequency is 2379 + n MHz, where n is the value of this register, and n can be from 0 to 116.
This gives a frequency range from 2379 MHz to 2495 MHz. Note that this frequency range extends
beyond the ISM band.
If PRF_CHAN.FREQ is set to 127, and for the RX and TX test commands, the frequency must be
programmed directly in hardware registers. In this case, the synthesizer frequency is set by programming
the 7-bit frequency word located in FREQCTRL.FREQ[6:0]. The synthesizer frequency is given by
2379 + n MHz, where n is the value of FREQCTRL.FREQ[6:0], and is programmable in 1-MHz steps.
The device supports synthesizer frequencies in the range from 2379 MHz to 2495 MHz. The usable
settings for FREQ[6:0] is consequently 0 to 116.
In RX, the system operates on a low intermediate frequency (IF) of 1 MHz for data rates up to 1 Mbps,
and on a zero IF for 2 Mbps. In TX, the system supports operating on low IF or zero IF. The IF to be used
for TX can be programmed in the register MDMTEST1.TX_TONE. The receiver may operate on a positive
or negative IF when the data rate is 1 Mbps and lower; this is controlled with MDMTEST1.RX_IF.
When the symbol rate is 1 Mbps or lower and the LLE programs the frequency, it uses a ±1 MHz IF on
TX. For both RX and TX, a negative IF is used when PRF_CHAN.FREQ < 62, and a positive IF is used
when PRF_CHAN.FREQ ≥ 62
When the symbol rate is 2 Mbps and the LLE programs the frequency, it uses an IF on TX as specified in
PRF_RADIO_CONF.TXIF. This IF may be zero, or ±1 MHz, ±2 MHz, or ±3 MHz. The recommended
setting is ±1 MHz. A negative IF is used when PRF_CHAN.FREQ < 62, and a positive IF is used when
PRF_CHAN.FREQ ≥ 62.
For all data rates, the setting of MDMCTRL1.PHASE_INVERT is taken into account by the LLE when finding
the setting for MDMTEST1.TX_TONE. The FREQCTRL register is programmed corresponding to the
programmed IF in order to operate on the channel specified by PRF_CHAN.FREQ.

25.6 Modulation Formats

The CC2541 supports GFSK and MSK modulation formats. For GFSK modulation, the deviation can be
set to 160 kHz or 250 kHz (320 kHz or 500 kHz for 2 Mbps). The data rate can be set to 250 kbps, 500
kbps, 1 Mbps, or 2 Mbps. The desired modulation scheme is set in the MDMCTRL0.MODULATION register.
Not all combinations of modulation format, data rate and deviation are supported.
overview of supported combinations.
Table 25-10. Supported Modulation Formats, Data Rates, and Deviations
Modulation Format
GFSK
GFSK
GFSK
GFSK
GFSK
MSK
MSK

25.7 Receiver

When the receiver is started, it searches for the preamble and the sync word. These are used for
frequency offset compensation and bit and byte synchronization. The sync word can be programmed to be
from 16 to 32 bits.
296
CC2541 Proprietary Mode Radio
Data Rate
2 Mbps
2 Mbps
1 Mbps
1 Mbps
250 kbps
500 kbps
250 kbps
Copyright © 2009–2014, Texas Instruments Incorporated
Table 25-10
Deviation
MDMCTRL0.MODULATION
500 kHz
320 kHz
250 kHz
160 kHz
160 kHz
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SWRU191F – April 2009 – Revised April 2014
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