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This article describes connection between personal computers and calculators or electronic diaries (SF and CSF families) CASIO using integrated circuits MAX232 and MAX233.
The first purpose of serial ports was
making connection between PC and modem to transmit data over extensions.
Nowadays serial ports are used to connect other devices for example mouse,
measuring devices or printers. That is the reason why computers contain
several serial ports (COM1, COM2, ...). Transmitting is performed through
TXD lines and receiving through RXD lines. The rest of lines control the
process. Following special bits are used:
Description of integrated circuits MAX232 and MAX233
Integated circuit MAX232 by Maxim Integrated Circuits is a bidirectional converter RS-232 <=> TTL powered by +5V. Contains two RS-232 => TTL (CMOS) and two TTL (CMOS)=> RS-232 converters. Both invert the signals to achieve required output. Device has internal voltage multiplier and inverter. Multiplier uses capacitor C1 to multiply voltage +5V to +10V on capacitor C3 (output V+) and inverter C2 to invert voltage +10V to -10V on capacitor C4 (output V-). Recommended value is 1 uF. Circuit MAX233 is a 20-pin version of the 16-pin MAX232, which has these 4 capacitors built in. Both circuits support transmission speeds up to 120 kb/s, various packages are available (pay attention to different pinouts of the DIP and SO packages of MAX233) Maxim also makes integrated cicuits MAX232A and MAX233A, which are different from presented types only in higher transmission speed - 200 kB/s- and lower values of capacitors - 0.1 uF.
Cable construction, design, gadgets specification
Power for integrated
circuit is supplied by 78L05, which is capable of supplying current up to
100 mA. Capacitor C5 is used for prevention against oscillations of 78L05
output voltage. Since DTR is connected to +12V and RTS to -12V, only one
of the two converters in MAX232 and MAX233 is used. Although Maxim
recommends value of external electrolytical capacitors 1 uF for MAX232 and
0.1 uF for MAX232A, I have used 4.7 uF because I had some of them at home.
Connection also works with higher capacitors, for example 22 uF and fits
into 25pin connector package.
MAX233 device is longer than the MAX232 of about one fifth of an inch,
but we don't have to use four capacitors.
I recommend using the MAX232 design, it is cheaper.
1x diode 1N4148
Connection of two calculators or two diaries
Instead of the expensive cable SB-62, which is used for connection of two calculators or two diaries, you can create its equivalent much cheaper. It is only a cable with two stereo jacks 2.5 mm, with transmit and receive signals crossed (R to T, T is on the tip of jack):
Here you can download communication program CASIO Program-link
FA-122 ver. 1.00 for Windows (only for types FX-7400G, CFX-9850G and
CFX-9930GT, types FX-9700GE and CFX-9800G can receive only). Other types
are supported by FA-121, which is not freeware. FA-122 has internal simple
program editor for comfortable work. It also has one disadvantage -
there's no compiler, so you still have to download programs to the
calculator when programming. File size is 523kB, author Casio Computer
CASIO Program-link :
Graphics Calculator Programs, Casio CFX-9850G Programs, Sanoy's Casio Programs, SilverSTone Casio fx Support, MadManu's CASIO Home Page, Rolf Klausens Casio Site, CasioGazette-The Happy Parrot Casio New Sletter Casio Link Site
Here you can download communication programs CASIF/WIN ver. 1.9e
for Windows (shareware) and Diary Link 97 for Windows 32bits (demo). Both
have very good graphic processing and provide comfortable adjustment of
enviroment. First of them has size of 1.5 MB and offers fully functional
enviroment, reminds to register on startup. Author is IMSL Software.
Second one uses BDE (Borland Database Engine) for operating with databases
and its author is Integrated Engineering Systems cc. Installation of this
program takes up about 5 MB of disk space. Since it is a demo version, it
has one big disadvantage. You can not transmit a group of items, only one
by one More information is at www.jamesralph.com/jr_diglink.html
CASIF/WIN ver. 1.9e for Windows
Written by: Michal Prazan
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