Liberty Basic is develeopped by Carl Gundel Original Newsletter compiled by Alyce Watson and Brosco Translation to HTML: Raymond Roumeas
In this issue:
Serial Communications by Herman
In future issues:
Thunking 32-bit API Calls
Contact Herman Oosthuysen:
http://www.AerospaceSoftware.com mailto:aerosof-@aerospacesoftware.com
General
There is a lot of mystique surrounding the PC serial port, simply because Microsoft never created a proper serial port driver.
The BASIC interpreter uses the bad Microsoft driver and therefore doesnt work all that well. Although one can get it to work, and it is useable, any serious application requires the use of a third party DLL.
That being said, this example shows how to use the LB serial port interface for those masochists out there who want to know why they should not use it...
Get a Plug
Firstly, we need to discuss a little hardware matter of plugs and things.
The PC comes with either a 25 or a 9 pin serial connector. You will need to plug into it and loop it back, so that we can talk to ourselves. Talking to oneself is usually not recommended, since one cannot learn anything new, but this is an exception!
Here is a list of the interesting pins on these connectors. Ignore the other pins, leave them unconnected.
9-pin Connector (Male at PC) 25-pin Connector
1 CD Carrier Detect (Its life Jim...) 8 2 RX Receive (...hlab ,hlaB) 3 3 TX Transmit (Blah, blah...) 2 4 DTR Data Terminal Ready (Local PC ready) 20 5 GND Ground - common (Terra firma) 7 6 DSR Data Set Ready (Remote equipment ready) 6 7 RTS Request to Send (I beg yours?) 4 8 CTS Clear to Send (Shoot!) 5
In order to keep the Windows serial driver happy, we have to interconnect some pins. So, you have to visit your local Radio Shack and stock up on connectors, hook-up wire, thin rosin flux solder solder and a soldering iron. (and some blistex if you are not used to soldering...).
Dont use a soldering gun - those things are for plumbers, not budding electrotechnicians. An ElCheapo 15 or 30W soldering iron would work fine.
The PC normally uses a male connector, so to interface to it, you need a female connector of the correct size. Your PC may even have both types of connector on the two communications ports.
Connect the following pins together:
RTS to CTS Ensures that CTS is always true DTR to both of DSR and CD Ensures that DSR and CD are always true RX to TX Loop back data so we can talk to ourselves
A loop-back connector like this is always very handy, so you can just as well make a good job of it and screw on a backshell and mark it as a loop-back test connector for future reference.
Which is Which?
Now, one of those two serial ports is COMM1 and the other is COMM2, but which one? Well, you can go hunt for the PC manual, or you can go the easy(?) way out and simply try it and see.
If you select the try and see method, you need a copy of Procomm or HyperTerminal. HyperTerminal is a buggy little program shipping free with Windoze, so if all else fails, use that one and since it was free, don't expect too much.
What you need to do is configure the program for a local connection, at whatever speed etc you please. Essentially, put your finger on a key and keep it down, if the port works, you will see a stream of characters coming back at you via your loop-back connector. After a while of fiddling and swearing, you should know which connector is COMM1 and which is COMM2.
Your modem is probably set up as COMM3, a common convention.
Now for the Super Duper Liberty BASIC Teletypewriter!
Once you have proven that the serial port works, you have to close the serial comms program and it may even be a good idea to reboot your PC at this point. With reboot, I mean full power off/on, since thanks to another common oversight in the design of PCs, the UART can lock up beyond salvage from Windoze. To add to your woes, the Windoze driver can also get stuck from time to time, and may tell you that the port is already in use or some other useless complaints, in which case you also have to reboot the PC, to convince Windoze that the port isnt in use after all and is in fact working just fine...
If you get "The device is already open" try closing all DOS boxes, then quit and restart LB. When all else fails, reboot your PC.
Finally, you can run the little program tty.bas. This program shows how to open the serial port and send something interactively. The main problem with this program is that it halts at an input statement, waiting for a user command which means that one cannot see any data coming in from another device, until one would press Enter. If you are talking to yourself with a loopback connector then this is not a problem, but see what happens when you tie two PCs together!
Connecting 2 PCs Together
Right, now that you got that going and want to go on to more adventurous things...
To connect 2 PC together, you need a NULL modem cable. That is literally a cable with no modem in the middle. I would suggest that you start your experiments with a single PC and 2 comm ports. In the above example, we used a single comm port. If you open both comm ports, then you can send messages from COMM1 to COMM2 and vice versa and test out your cable in the process, without getting two PCs locked up, which saves a lot of time on rebooting...
A NULL Modem Cable
There is an almost infinite number of ways to make such a cable. The simplest method is a variation of the loopback plug.
Connect the following pins together on each connector:
RTS to CTS DTR to both CD and DSR
Then run 3 wires (2 or 3 meters, whatever is convenient to reach the other PC) between the two connectors for your data connection:
GND to GND RX to TX TX to RX
These data wires can be up to 25 meters in length and still allow reliable operation.
Now, with some work, you can send files between the PCs, or write your own LAN.
Have fun,
Herman http://www.AerospaceSoftware.com
'Name: TTY.bas 'Description: Serial Terminal Demonstration Program 'Copyright (c) 1999, Aerospace Software Ltd., Calgary, Canada 'You may use this program freely '********************************************************************* 'declarations serial = 0 'serial port file handle tty = 0 'terminal window file handle rxdata$ = "" 'receive data txdata$ = "" 'transmit data length = 0 'receive data length wait = 0 'delay counter '********************************************************************* 'Name: main 'Description: Main terminal loop 'inputs: none 'Outputs: #tty ' #serial '********************************************************************* [main] 'center the window if the screen is larger than the default WindowWidth = 640 WindowHeight = 480 UpperLeftX = (DisplayWidth - WindowWidth) / 2 UpperLeftY = (DisplayHeight - WindowHeight) / 2 if UpperLeftX <= 0 then UpperLeftX = 0 end if if UpperLeftY <= 0 then UpperLeftY = 0 end if 'open the comm port open "COM1:9600,N,8,1" for random as #serial 'test the serial comms gosub [commtest] 'forever... [main_loop] 'poll the window for keyboard input gosub [transmit] 'poll the serial port for data input gosub [receive] if (TrapClose = "true") goto [quit] goto[main_loop] '********************************************************************* 'Name: transmit 'Description: Get a string from a text window ' and echo it out the serial port 'Inputs: #tty ' #serial 'Outputs: txdata$ '********************************************************************* [transmit] 'Wait for user input. 'Note that data may be coming in while you are stuck in the input 'function and you'll only see it when you press Enter. input "Transmit>"; txdata$ 'print the string to the main window 'and the serial port if (len(txdata$) > 0) then 'transmit the data print #serial, txdata$ 'wait for the data to be transmitted and received for wait = 0 to 1000 step 1 next wait end if return '********************************************************************* 'Name: receive 'Description: Get character(s) from the serial port ' and echo it (if any) to the text window 'Inputs: #serial ' #tty 'Outputs: rxdata$ ' length '********************************************************************* [receive] length = lof(#serial) if (length > 0) then trace 2 rxdata$ = input$(#serial, length) print rxdata$ end if return '********************************************************************* 'Name: commtest 'Description: test routine 'Inputs: #serial ' #tty 'Outputs: rxdata$ ' length ' wait '********************************************************************* [commtest] 'send a data string print #serial, "Yahoo!" 'wait for it - 1ms per character at 9600 bps for wait = 0 to 1000 step 1 next wait 'read the receive buffer length = lof(#serial) 'print it if anything was received if (length > 0) then rxdata$ = input$(#serial, length) print rxdata$ end if return '********************************************************************* 'Name: quit 'Description: close the window and serial port 'Inputs: #serial ' #tty 'Outputs; none '********************************************************************* [quit] 'close the comm port close #serial end '******************************* EOF *********************************
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