I was aware when I bought the Z88 that it connected readily to a BBC or a PC but there was, not surprisingly, no mention of the Elk. (It also connects readily to a printer with a parallel or serial port, coincidentally.)
The first requirement for the computer to computer link was an RS423 on the Electron. I have the RS423 COMMUNICATION CARTRIDGE from Pace Micro Technology that I use with a modem utilising the COMMSTAR software provided in the cartridge. The comm cartridge has a five-pin domino plug fitted on the end of a cable. This plugs directly into the modem.
My first job was to make a lead connecting from the Z88 to the domino plug. Domino plugs are designed to fit either of two ways. I don't know why. One must be careful to connect it the right way round. On making the lead, I found that the kitset nine-pin Dplug had a "nose" that held the end plate in place. This prevented the plug from inserting fully into the socket because the socket on the Z88 fits flush. Bought an IBM monitor extension lead (which has a male nine-pin D at one end and a female nine-pin D at the other with straight through connections). My made-up lead then connected fully.
Hey presto! Nothing happened. The computers weren't talking to each other. I read what there was in the Z88 handbook. It had the pinouts for its RS232C port and the connections at the other end for a serial printer using a 25-pin Dplug. The COMMSTAR handbook gave the pinouts for its domino plug. I pondered over these for some time. I thought I knew a little about computers but there was a lot still to be learnt. So, at this stage, things that were obvious later on were not so obvious.
One developed a little familiarity with terms like RX (Receive from distant station), TX (Transmit to distant station), CTS (Clear to send) and RTS (Ready to send). Well, it wasn't and it didn't. I was told that RX from one machine had to be connected to TX on the other (Moderms do this for you!) and similarly with CTS and RTS. Ground, of course, had to stay with ground. Then there is the baud rate which is the rate at which data is transmitted over a serial link. The sender and receiver must be set to the same baud rate. Then there are protocols such as Xon/Xoff and parity to be set.
At this stage I was using the COMMSTAR software at the Elk end and I was trying to send files each way. My wish was to be able to use the Z88 on business trips and be able to transfer files to the Elk for storage and printing out. I could print directly from the Z88 but couldn't store files reliably. The Z88 I purchased had 128K of memory in slot 3 and this slot uses more power than the other two. I kept running out of battery which, on a Z88, means losing any suspended files and in extreme cases losing all data. So I prefered being able to transfer files.
I'll skip a little trivia which involved much gnashing of teeth and racking of brains. Eventually I got to the stage of being able to type characters on the Z88 keyboard and have them appear on the Electron's screen, using COMMSTAR's chat mode. And vice versa. This is partly related to something called echo. COMMSTAR allows echo to be switched on or off but the Z88 has no facility for this. When a character is sent to another computer, either directly as in my case, or via a modem, the receiving computer sends an echo back and this is what appears on the screen of the sender's computer. When this echo is not available echo can be switched on so that the sender also writes to its own screen.
I still couldn't send files although I could see that the Z88 was trying by giving a block count but all COMMSTAR said was "Multiple errors, retry?" which still didn't work. Later I came across a note deep in the handbook that said CTS and RTS must be connected together when connecting directly with another computer. This helped.
I then got together with a friend who has a Z88 and a BBC and we checked a few things such as how the Z88/BBC link was connected. More modifications and more progress. However the real breakthrough came from ignoring the COMMSTAR software and using the RS423 cartridge simply as an RS423 port and using other software. I was given several communication programs and these seem to work as well in the Electron as in the BBC. Z88ix works, as does PC LINK II from The Micro User. I transferred my first file! It wasn't quite the same as the original but it felt like the home run.
About this time I dismantled the Pace cartridge to find that RTS had never been connected to the board! I assumed it should be as the COMMSTAR handbook quotes an RTS pinout at the domino plug. I have since connected it and can now send files both ways. This is about as far as I have gone. I believe I have to produce an ASCII Pipedream file for transfer without problems and probably the same the other way.
As I said at the beginning, if someone reading this has already been down this path, I'd love to hear from him as I need to spend more time on it to have it running the way I would like. It's been a great learning experience and makes my system more useful to me. I omitted to say that I have the PC Link cartridge in my Z88 which is necessary for running the PC LINK II program.
Alan Richardson, EUG #26