1200/2400/4800bps MSK Modem
6
MX469
3. External Components
VDD
XTAL/CLOCK
VDD
C7
R1
X1
C6
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
CARRIER DETECT TIME CONSTANT
XTAL
C1
TX SYNC OUT
TX SIGNAL OUT
TX DATA IN
CLOCK RATE
C4
4800 BPS SELECT
1200/2400 BPS SELECT
RX SYNC OUT
MX469
TX ENABLE
VDD
C3
BANDPASS OUT
RX ENABLE
RX SIGNAL IN
C5
CARRIER DETECT OUT
CLOCKED DATA OUT
UNCLOCKED DATA OUT
VBIAS
VSS
C2
Figure 2: Recommended External Components
Component
Notes
Value
Tolerance
R1
C1
C2
C3
C4
C5
C6
C7
X1
±10%
±5%
1.0Mꢂ
33pF
1.0µF
±20%
0.1µF
±20%
Note 1
Note 2
Note 3
Note 2
Note 4
0.1µF
±10%
1.0µF
33pF
±25%
±5%
1.0µF
±20%
1.008MHz or 4.032MHz
See ‘Clock-Rate’ Pin
Table 4: Recommended External Components
Notes:
1. The value of C4 determines the Carrier Detect time constant. A long time constant results in improved
noise immunity but increased response time. C4 may be varied to trade-off response time for noise
immunity.
2. Decoupling circuits depend upon whether the input signal is referenced to V
or V . Use C5 when
SS
BIAS
the input signal is referenced to V . Use C7 when the input signal is referenced to V . It is not
BIAS SS
necessary to use both C5 and C7.
3. C6 reduces Xtal voltage overshoot. Reference the MX-COM Xtal Application Note.
4. For best results, a crystal oscillator design should drive the clock inverter input with signal levels of at
least 40% of V , peak to peak. Tuning fork crystals generally cannot meet this requirement. To
DD
obtain crystal oscillator design assistance, consult your crystal manufacturer.
ꢀ1998 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480081.010
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CMLMICRO [ CML MICROCIRCUITS ]
