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PDF CMX909B Data sheet ( Hoja de datos )
| Número de pieza | CMX909B | |
| Descripción | GMSK Packet Data Modem | |
| Fabricantes | Consumer Microcircuits Limited | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de CMX909B (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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CML Microcircuits
COMMUNICATION SEMICONDUCTORS
CMX909B
GMSK
Packet Data Modem
D/909B/2 November 2008
Features
• GMSK Modulation/Demodulation • On-chip Packet Detection
• Rx or Tx up to 38.4kbits/sec
• Parallel Host Processor Interface
• Full and Short Data Packet Framing • Low Power 3.0V/5.0V Operation
• Mobitex Compatible including
R14N Short Block Frames
• Flexible Operating and Powersave
Modes
1. Brief Description
The CMX909B is a half-duplex Gaussian Minimum Shift Keyed (GMSK) BT=0.3 modem data pump with
on-chip packet data handling. GMSK modulation optimises the data throughput for a given bandwidth RF
channel and the on-chip packet data handling relieves the host µC of regular processing tasks, such as
maintaining Bit and Frame Synchronisation, Block Formatting, CRC and FEC Error Processing, Data
Interleaving and Scrambling. The demodulator uses decision feedback equalisation techniques to reduce
the channel distortion effects and enhance the receiver performance without the computational overhead
of maximum likelihood (Viterbi) estimation methods.
The CMX909B is pin, function and software backwards compatible with the FX909A and MX909A
modems and also uses the same external components. It offers improved performance, higher data rates
and lower voltage operation, as well as handling the recent R14N extension to Mobitex for short block
frames. The CMX909B also offers 2-strength Xtal driver circuitry – for wider choice of xtals, optional zero-
error or one-error frame sync. detection, multiple powersave options – for intelligent power management,
and availability in both 24-pin TSSOP and SSOP low-height package options.
The CMX909B is ideally suited to wireless data applications such as Mobitex terminals, wireless
telemetry, licence-free radio data and ISM band radio schemes.
© 2008 CML Microsystems Plc
1 page  
GMSK Packet Data Modem
2. Block Diagram
CMX909B
Figure 1 Block Diagram
© 2008 CML Microsystems Plc
5
D/909B/2
5 Page 
GMSK Packet Data Modem
CMX909B
adjustment circuitry. The ground connection to the capacitor C5 should be positioned to give
maximum attenuation of high frequency noise into the modulator. R4 and C5 should be chosen
so that the product of the resistance of R4 (in Ohms) and capacitance of C5 (in Farads) is
0.34/bit rate (bit rate in bits per second). R4 should be not less than 47kΩ and the value used
for the external capacitor should take into account parasitic capacitance.
Suitable values being:
R4 C5
8000 bits/sec
100kΩ 430pF
4800 bits/sec
100kΩ 710pF
The signal at the TXOP pin is centred around VBIAS and is approx 0.2 x VDD pk-pk, going
positive for a logic ‘1’ and negative for a logic ‘0’, if the modem is not inverting the Tx data.
A capacitor may be fitted if ac coupling of the input to the frequency modulator is desired, see
section 6.4.
The ‘eye’ diagram of the transmitted signal (after the external R4/C5 network) is shown in
Figure 5.
Figure 4 Typical Modem µC Connections
© 2008 CML Microsystems Plc
11
D/909B/2
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet CMX909B.PDF ] | |
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