4-Level FSK Modem Data Pump
FX919A
1.4
External Components
Figure 2 Recommended External Components
R1
R2
R3
R4
X1
See Section 1.5.1
100k ohm
±
5%
1M ohm
±
20%
100k ohm
±
5%
See Section 1.5.5.3
C1
C2
C3
C4
0.1 µF
±
20%
0.1 µF
±
20%
±
20%, see Note 1
±
20%, see Note 1
C5
C6
C7
C8
±
5%, see Note 3
±
20%, see Note 2
±
20%, see Note 2
±
5%, see Note 3
Note 1: The values used for C3 and C4 should be suitable for the frequency of the crystal X1.
As a guide, values (including stray capacitances) of 33pF at 1MHz falling to 18pF at 10MHz will
generally prove suitable. The 'Phase-Locked Loop Modes' part of section 1.5.5.3 discusses crystal
frequency tolerances.
Note 2: C6 and C7 values (in nano Farads) should be equal to 50000
÷
symbol rate, e.g.
Symbol Rate
2400 symbols/second
4800 symbols/second
9600 symbols/second
C6/C7 (nF)
22.0
10.0
4.7
Note 3: C5 and C8 values (in pico Farads) should be equal to 750000
÷
symbol rate, e.g.
Symbol Rate
2400 symbols/second
4800 symbols/second
9600 symbols/second
C5/C8 (pF)
330
150
82
©
1996 Consumer Microcircuits Limited
6
D/919A/4
CMLMICRO [ CML MICROCIRCUITS ]
