MX614 データシートの表示（PDF） - MX-COM Inc
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MX614 Datasheet PDF : 19 Pages
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Bell 202 Compatible Modem
6
4. General Description
MX614 PRELIMINARY INFORMATION
4.1 Xtal Osc and Clock Dividers
Frequency and timing accuracy of the MX614 is determined by a 3.579545MHz clock signal present at the
XTAL/CLOCK pin. This may be generated by the on-chip oscillator inverter using the external components
C1, C2 and X1 of Figure 2, or may be supplied from an external source to the XTAL/CLOCK input. If supplied
from an external source, C1, C2 and X1 should not be fitted.
The on-chip oscillator is turned off in the 'Zero-Power' mode.
If the clock is provided by an external source which is not always running, then the 'Zero-Power' mode must
be set when the clock is not available. Failure to observe this rule may cause a significant rise in the supply
current drawn by MX614 as well as generating undefined states of the RXD, DET and RDY outputs.
4.2 Mode Control Logic
The MX614's operating mode is determined by the logic levels applied to the M0 and M1 input pins:
M1
M0
0
0
0
1
1
0
1
1
[1] If enabled
Rx Mode
Tx Mode
1200bps
150bps
Off
1200bps
1200bps
Off / 5bps
'Zero-Power'
Data Retime[1]
Rx
Tx
Rx
-
Note: On applying power to the device, the mode must be set to 'ZP', i.e. M0 = '1', M1 = '1', until VDD
has stabilized.
In the 'Zero-Power' (ZP) mode, power is removed from all internal circuitry. When leaving the 'ZP' mode there
must be a delay of 20ms before any Tx data is passed to, or Rx data read from the device to allow the bias
level, filters, and oscillator to stabilize.
4.3 Rx Input Amplifier
This amplifier is used to adjust the received signal to the correct amplitude for the FSK receiver and Energy
Detect circuits (see section 5.1).
4.4 Receive Filter and Equalizer
The Receive Filter and Equalizer section is used to attenuate out of band noise and interfering signals,
especially the locally generated transmit tones which might otherwise reach the 1200bps FSK Demodulator
and Energy Detector circuits. This block also includes a switchable equalizer section. When the RXEQ pin is
low, the overall group delay of the receive filter is flat over the 1200bps frequency range. If the RXEQ pin is
high the receive filter's typical overall group delay will be as shown in Figure 3.
2000 MX-COM, INC.
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480162.004
4800 Bethania Station Road, Winston-Salem, NC 27105 USA
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