1200/2400/4800bps MSK Modem
6
MX469
3. External Components
V
DD
XTAL/CLOCK
X1
C1
C6
R1
XTAL
TX SYNC OUT
TX SIGNAL OUT
TX DATA IN
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
V
DD
C7
CARRIER DETECT TIME CONSTANT
CLOCK RATE
4800 BPS SELECT
1200/2400 BPS SELECT
RX SYNC OUT
RX SIGNAL IN
C3
C4
V
DD
TX ENABLE
BANDPASS OUT
MX469
C5
RX ENABLE
CARRIER DETECT OUT
CLOCKED DATA OUT
UNCLOCKED DATA OUT
V
BIAS
MX469P package discontinued
V
SS
C2
Figure 2: Recommended External Components
Component
R1
C1
C2
C3
C4
C5
C6
C7
X1
Notes
Value
1.0M
33pF
1.0µF
0.1µF
Tolerance
±10%
±5%
±20%
±20%
±10%
±25%
±5%
±20%
See ‘Clock-Rate’ Pin
Note 1
Note 2
Note 3
Note 2
Note 4
0.1µF
1.0µF
33pF
1.0µF
1.008MHz or 4.032MHz
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
BIAS
or V
SS
. Use C5 when
the input signal is referenced to V
BIAS
. Use C7 when the input signal is referenced to V
SS
. It is not
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
DD
, peak to peak. Tuning fork crystals generally cannot meet this requirement. To
obtain crystal oscillator design assistance, consult your crystal manufacturer.
1998
MX-COM, Inc.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480081.010
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
All trademarks and service marks are held by their respective companies.
CMLMICRO [ CML MICROCIRCUITS ]
