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MZ-700 Modems 
written by Tim Cowell / SUC/UK
Source: SUC-magazine March 1988, Volume 8, Number 2, pp. 48 - 49 


Following the article in Vol 8 No. 1 there has been some interest shown in the modem project. In fact some people are actually making the interface themselves and have spotted one or two silly mistakes in the published circuit diagram. The corrected diagram is given in this issue ( Comment by The previous page is already corrected ).
Errata The circuit diagram of 22 / 2 / 88 incorrectly marked the 1489 and the 7404 chips, there were also some incorrect pin numbers on these chips.


I have written Version 1 of a simple communications program which uses the serial interface. The program as yet has no title page so for want of anything better will be referred to as 'SHARP TALK‘. I have used 'SHARP TALK‘ successfully with a couple of modems to talk to the Mektronics Fido and Telecom Gold bulletin board services. Before going into the detail of the
program I will firstly describe a little about Viewdata and Bulletin Boards..

Viewdata is a communications protocol used mainly in the U.K for displaying graphics and colour using a 7 bit ASCII code. It has become popular as a standard with such users as PRESTEL, the travel agency networks and other private firms, i.e. KAYS mail order and FORDS dealer network using it. Unfortunately for SHARP users it is not simple to display on Sharp machines because the graphic characters required do not exist on machines like the MZ700 or MZ80K etc. Because of this I have not aimed at providing a package for use with these type of services but have concentrated at the more conventional bulletin board services..

Bulletin boards for those unfamiliar with the term are like electronic newspapers, except that you can write in them as well as read them, and then other people can read what you have written. This allows people to exchange ideas, hold debates and swap files electronically. Most bulletin boards are easy to use and provide a menu driven front display with help information available. These too can be colourful and provide a limited use of graphics using a different protocol known as ANSI. ANSI is a worldwide standard for sending control information like colours and screen positioning. The ANSI standard does not use special characters however so is much more suited to machines like the MZ700. For this reason I have tailored ‘SHARP TALK' to the ANSI system.


This is a terminal emulation program using Channel A of the SUC Z80 Serial Interface ( or Peterson Electronic TO3 ). This means that it can send data from the MZ700 keyboard to the serial interface and receive data from the serial interface and display it on the screen. The keyboard behaves as a normal typewriter keyboard, i.e. SHIFT converts to upper case, and all keys have an auto-repeat. The CTRL key when pressed in conjunction with an alphabetic key sends the corresponding control code, i.e. CTRL and ‘A' sends ASCII code 01. The blank key above CR sends the ESCAPE character ( ASCII code 27 ). All other keys send the true ASCII codes, not the SHARP ASCII codes, and so are compatible with all other bulletin boards. The screen is 80 columns by 24 lines of which any 40 columns is displayed at once. The 40 columns being displayed can be moved left and right over the 80 columns very quickly by holding down the CTRL key and pressing the cursor left and right keys. The 25th line is left blank and is to be used as a status / menu line. The SIO is programmed for 8 data bits, 1 stop bit and No Parity, this works with most bulletin boards, even those requiring 7 bit data with parity. There are as yet no built in file transfer protocols. For the technically minded the emulator supports ANSI control codes and can handle random cursor addressing / cursor movement / clear screen / colour setting and some of the ‘IBM‘ graphic character set. This produces very nice colourful displays with some of the better bulletin boards. The program is written in less than 2k of machine code ( actually compiled from ‘C‘ ) and so loads very quickly. By the time you read this there will also be a setup menu allowing the changing of 7 / 8 data bits, 1 / 2 stop bits, Even / Odd / No parity, Channel A / Channel B, Full / Half Duplex and Carriage Return translation. Maybe even a flashy front page display ?

I will send Roy Houghton a copy of the existing program and the version with the setup menu, anybody wanting a copy can then do so via the usual library means. Alternatively they can send me a blank tape and SAE and 2 first class stamps ( to cover photocopy costs ) and I will send the latest version plus a list of over 50 public bulletin boards.

Later enhancements planned are ‘DTR‘, ‘RTS‘ / ‘CTS‘ control, sending of BREAKS ( long space ), logging to printer and ‘frame store' / review. Eventually there will be an XMODEM protocol for file transfer but you may wait some time for that.

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last updated October 17, 2003
SUC / UK: Tim Cowell