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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. 

Serial ports 
Description of integrated circuits MAX232 and MAX233 
Cable construction, design, gadgets specification 
Connection of two calculators or two diaries 
Calculators - download of communication program, interesting links 
Diaries - download of communication program, interesting links 

Serial ports 

      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: 
Start bit - is the begining of a group of bits and is active low
Data bits - a group of 5, 6, 7, or 8 bits
Parity bit - tracks the number of '1' bits (high level), doesn't have to be present
Stop bit - terminates the bit sequence for transmitting one byte, always active high, there can be one or two of them present.
Electric characteristics of inputs and outputs are determines by the RS-232 standard, voltage levels are used. High level signals are represented by voltage +12V, low level signals -12V. The table shows pin descriptions of 9 and 25 pin connectors.

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.
Schematics with MAX232:

 

MAX233 device is longer than the MAX232 of about one fifth of an inch, but we don't have to use four capacitors.
Schematics with MAX233, DIP package :

 

I recommend using the MAX232 design, it is cheaper.

Partlist : 

1x diode 1N4148 
5x (1x) electrolytic capacitor 4,7 uF / 16 V
1x circuit 78L05
1x circuit MAX232 (MAX233) or equivalent
1x stereo jack 2.5 mm
1x cable at least 1 m long
1x female serial connector 25pin or 9pin
1x package for used connector

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):  

 

Calculators 

 Communication program 

 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 Co., Ltd..
 
 

CASIO Program-link :

Local mirror at HW.cz 
Original  : http://pegasus.cc.ucf.edu/~ucfcasio/link.zip 

 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 

Diaries (organizers) 

 Communication programs 

 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

Local mirror at HW.cz 
Original  : http://ourworld.compuserve.com/homepages/imsl/casifw19.zip 

Local mirror at HW.cz 
Original  : http://www.jamesralph.com/dldemo1.exe 

Links

Casio Digital Diary Communications Information Center
Tips on using Casio diaries and CASIF/WIN
FAQ (Frequently Asked Questions)