EV6240 Datasheet, PDF (16/47 Pages) CML Microcircuits – Opto-Isolated serial interface capability

Evaluation Kit for CMX624/CMX644A
1.6 Detailed Description
EV6240
1.6.1 Hardware Description - Evaluation Board
1.6.1.1 Line Protection.
Line protection is provided for each Modem on both line interfaces by R14-R19 (47Ω), R42-R47 (47Ω),
D12, D15, D16, D25, D28 and D29 (Phillips BR211 series 140V). These components are not fitted,
but suitable values for UK applications are suggested in brackets. Wire links which bypass R14-R19
(Modem One) and R42-R47 (Modem Two) will need to be removed if these resistors are fitted.
1.6.1.2 Operating Voltage
The operating voltage (V_DD) is set to 5.0V. This may be altered by changing components R4 and R5
which are socketed. To select 3.3 Volts set R4 = 360Ω and R5 = 33Ω. The formula for calculating the
values of R4 and R5 is as follows:
R4 + R5 = ^{240 (VDD −1.25)}
1.25
Where 240 is the value of R7 in ohms and V_DD is the required supply voltage.
1.6.1.3
Clock/Oscillator
The CMX6x4 evaluation devices may use either an external clock or their own xtal oscillators. Two
on-board xtals, 3.5795MHz (CMX624) and 3.6864MHz (CMX644A), are provided for each Modem
for the latter method. A single switch for each Modem is provided to select between the on-board
xtals, SW5 (Modem One) and SW9 (Modem Two). Two jumpers for each Modem (JP3 and JP4 for
Modem 1 and JP6 and JP7 for Modem 2), which are normally fitted, can be removed to allow for an
external clock. The external clock may be supplied to JP4 pin 1 (Modem One) and/or JP7 pin 1
(Modem Two) once the jumpers have been removed.
The PIC16C77 may be provided with an external clock in the same way by removing jumpers JP1
and JP2. Note that PICs programmed by CML are only configured for use with the on-board 4MHz
crystal.
1.6.1.4
Line Interface
Each Modem is provided with 2-wire and 4-wire line interfaces. The interfaces for each Modem are
selected using two miniature switches, SW4 and SW6 (Modem One) and SW7 and SW8 (Modem
Two).
The line interface switches should be the same as the settings in the S27 registers.
The majority of the line interface components are fitted in sockets for adjustment purposes. These
values should be calculated based on the evaluation device, operating voltage and line conditions,
see the evaluation device data sheet for more information. The 2-wire ac line impedance matching is
provided by T1, R26 (Modem One) and T4, R54 (Modem Two) which are factory fitted to suit a 600Ω
line.
The line transformers used on the EV6240 board have an insertion loss of approximately 1.2dB over
the operating frequency range.
The dc line resistors, R20 (Modem One) and R48 (Modem Two) should be removed when
connecting the on-board Modems together via the 2-wire line.
Note: for correct operation ensure the TXON output of the CMX6x4 device is enabled whilst
performing evaluation tests.
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© 1999 Consumer Microcircuits Limited
UM6240/3