FX614 Consumer Microcircuits Limited, FX614 Datasheet - Page 6

• Manufacturer Part Number: FX614
• Description: Bell 202 Compatible Modem Fx614
• Manufacturer: Consumer Microcircuits Limited

Bell 202 Compatible Modem
1.5.2
The FX614's operating mode is determined by the logic levels applied to the M0 and M1 input pins:
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 stabilise. On applying power to the device the mode must be set to 'ZP', i.e. M0 =
'1', M1 = '1', until V
1.5.3
This amplifier is used to adjust the received signal to the correct amplitude for the FSK receiver and Energy
Detect circuits (see section 1.6.1).
1.5.4
Is used to attenuate out of band noise and interfering signals, especially the locally generated transmit tones
which might otherwise reach the 1200bits/sec FSK Demodulator and Energy Detector circuits. This block also
includes a switchable equaliser section. When the RXEQ pin is low, the overall group delay of the receive filter
is flat over the 1200bits/sec frequency range. If the RXEQ pin is high the receive filter's typical overall group
delay will be as shown in Figure 3.
1997 Consumer Microcircuits Limited
Mode Control Logic
Rx Input Amplifier
Receive Filter and Equaliser
M1
0
0
1
1
[1] If enabled.
M0
0
1
0
1
DD
has stabilised.
Figure 3 Rx Equaliser Group Delay (RXEQ = '1') wrt 1700Hz
1200bits/sec
1200bits/sec
Rx Mode
Off
'Zero-Power'
6
Off / 5bits/sec
1200bits/sec
150bits/sec
Tx Mode
Data Retime [1]
Rx
Rx
Tx
-
D/614/4
FX614