CML Semiconductor Products
Wireless Modem Data Pump
1.0
Features
FX909A
D/909A/4 March 1996
Provisional Issue
•
GMSK Modulation
•
Rx or Tx up to 19.2k bits/sec
•
Full Data Packet Framing
•
Mobitex Compatible
•
Flexible Operating Modes
•
Host Processor Interface
•
Low Power 3.3V/5V Operation
•
24-Pin Small Form Package Option
1.1
Brief Description
The FX909A is a CMOS integrated circuit that contains all of the baseband signal processing and
Medium Access Control (MAC) protocol functions required for a high performance GMSK Wireless
Packet Data Modem. It interfaces with the modem host processor and the radio
modulation/demodulation circuits to deliver reliable two-way transfer of the application data over the
wireless link.
The FX909A assembles application data received from the processor, adds error correction code
(FEC), adds error detection code (CRC), time-spreads this data by interleaving (burst-error
protection) and scrambles (randomises) the bit pattern. After adding bit and frame sync codewords,
it converts the packet into analogue GMSK signals for modulating the radio transmitter.
In receive mode, the FX909A performs the reverse function using the analogue signals from the
receiver discriminator. After error correction and removal of the packet overhead, the recovered
application data is supplied to the processor. Any residual uncorrected errors in the data will be
flagged. A readout of the SNR value during receipt of a packet is also provided.
The FX909A uses data block sizes and FEC/CRC algorithms compatible with the Mobitex Wide Area
Network over-air standard. The format used is suitable for other private applications which require
the high-speed transfer of data over narrow-band wireless links. The FX909A is programmable to
operate at most standard bit-rates from a wide choice of Xtal/clock frequencies.
©
1996 Consumer Microcircuits Limited
Wireless Modem Data Pump
FX909A
CONTENTS
Section
Page
1.0 Features.......................................................................................................... 1
1.1 Brief Description............................................................................................ 1
1.2 Block Diagram................................................................................................ 3
1.3 Signal List....................................................................................................... 4
1.4 External Components.................................................................................... 6
1.5 General Description....................................................................................... 7
1.5.1 Description of Blocks.................................................................... 7
1.5.2 Modem - µC Interaction.............................................................. 10
1.5.3 Data Formats ............................................................................. 11
1.5.4 The Programmer's View............................................................. 13
1.5.5 CRC, FEC, Interleaving and Scrambling Details........................ 29
1.6 Application Notes ........................................................................................ 32
1.6.1 Transmit Frame Example........................................................... 32
1.6.2 Receive Frame Example............................................................ 34
1.6.3 Clock Extraction & Level Measurement Systems ...................... 36
1.6.4 AC Coupling ............................................................................... 37
1.6.5 Radio Performance .................................................................... 39
1.7 Performance Specification ......................................................................... 40
1.7.1 Electrical Performance ............................................................... 40
1.7.2 Packaging .................................................................................. 45
©
1996 Consumer Microcircuits Limited
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D/909A/4
Wireless Modem Data Pump
FX909A
1.2
Block Diagram
Figure 1 Block Diagram
©
1996 Consumer Microcircuits Limited
3
D/909A/4
Wireless Modem Data Pump
FX909A
1.3
Signal List
Package
D2/D5/P4
Pin No.
1
Signal
Description
Name
IRQN
Type
O/P
A 'wire-ORable' output for connection to the host
µ
C's Interrupt Request input. This output has a
low impedance pull down to V
SS
when active
and is high impedance when inactive.
)
)
)
)
)
)
)
)
2
3
4
5
6
7
8
9
10
D7
D6
D5
D4
D3
D2
D1
D0
RDN
BI
BI
BI
BI
BI
BI
BI
BI
I/P
8-bit bidirectional 3-state
µ
C interface data
lines.
Read. An active low logic level input used to
control the reading of data from the modem into
the host
µ
C.
Write. An active low logic level input used to
control the writing of data into the modem from
the host
µ
C.
The negative supply rail (ground).
Chip Select. An active low logic level input to the
modem, used to enable a data read or write
operation.
)
)
Two logic level modem register select
inputs.
11
WRN
I/P
12
13
Vss
CSN
Power
I/P
14
15
16
17
A0
A1
XTALN
XTAL/CLOCK
I/P
I/P
O/P
I/P
The output of the on-chip oscillator.
The input to the on-chip oscillator, for external
Xtal circuit or clock.
)
)
)
Connections to the Rx level measurement
circuitry. A capacitor should be connected
from each pin to V
SS.
18
19
DOC 2
DOC 1
O/P
O/P
©
1996 Consumer Microcircuits Limited
4
D/909A/4
Wireless Modem Data Pump
FX909A
Package
D2/D5/P4
Pin No.
20
21
Signal
Description
Name
TXOP
V
BIAS
Type
O/P
O/P
The Tx signal output from the modem.
A bias line for the internal circuitry, held at
½ V
DD
. This pin must be decoupled to V
SS
by a
capacitor mounted close to the device pins.
The input to the Rx input amplifier.
The output of the Rx input amplifier and the input
to the Rx filter.
The positive supply rail. Levels and voltages are
dependent upon this supply. This pin should be
decoupled to V
SS
by a capacitor.
22
23
RXIN
RXFB
I/P
O/P
24
V
DD
Power
Notes:
I/P =
O/P =
BI
=
Input
Output
Bidirectional
©
1996 Consumer Microcircuits Limited
5
D/909A/4
Embedded System
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