Edtasm came in two versions, cartridge and disk. Cartridge based Edtasm+ used the tape player for storage, Disk Edtasm could use either. Cartridge Edtasm+ was a good choice for 16K machines, Disk Edtasm would work in 16K, but 32K was definitely recommended. Disk Edtasm is capable of assembling larger programs than the rom based Edtasm, with the use of the INCLUDE command, as multiple disk source files can be assembled without all being in memory at the same time.
Edtasm+ Crash Course
Basic on the CoCo is a powerful language, but lack of memory space and slow execution times can be a problem. If I want to crank out a program in an afternoon, I write it in Basic. If I have a Basic program that has some slow spots in it, I will usually write an assembly routine and replace that portion of Basic code. Any serious work though, I do strictly in Assembly Language. The fastest most memory efficient programs are written fully in assembler. The assembler I have some experience with is Edtasm.
If you have the original documentation, what follows may seem brief. If you have no documents, this may be enough to get you going. Edtasm may seem intimidating at first, especially if you have never used Assembly Language before. When I started, I found writing small routines that modified video memory on the text screen provided a starting point to learn Edtasm and the basics of assembly language programming. What follows is not a course in 6809 assembly, but more on how to operate the Edtasm program itself.
1. Starting it up.
Cartridge version. Plug in the cartridge, then turn the CoCo on. Program will start automatically, in the Editor/Assembler mode.
Disk version. With the computer and drive on, and the Edtasm disk loaded, type RUN"DOS" at the Basic prompt. This loads in a cheesy version of DOS. A menu will appear, select the item to execute a program. Type in the program name, EDTASM, and it will then load and automatically start.
2. The Editor/Assembler
At startup, you will have an asterix (*) for a prompt. This lets you know you are in the Editor. To start inputting lines of code, type;
I <enter> This is the insert command. The editor will automatically pop up a line number, 00100 to start.You can now enter your line of code, which may consist of up to 4 fields.You can see the start of each field by using the right arrow key to tab between the fields. Alternatively use the left arrow key to tab backwards.
The first field is for the symbol. Every line of code does not require a symbol. The symbol can be up to 6 characters long. Use the right arrow key to tab over to the second field done once your symbol (if any) is named. The second field is always required, this is your command. The third field is for the operand, the fourth for your comments if any. Once your line of code is complete, press <enter> and the Editor will advance to the next line ,00110.
Once your lines are complete, stop the Insert mode by pressing <break>. You will then be at the * prompt. If you are like me, you will want to edit your listing. Edtasm's editor is a lot more useful than the editor in Extended Basic. Here is a list of commands;
|A||Assemble||See Lesson 3 for a description.|
|C||Copy||Copies a range of lines to a new location. Must include startline, range and increment. For example;
|D||Delete||Deletes a line or range of lines. For example;
|E||Edit||Edits a line. For example;
|F||Find||Finds a string of characters. For example;
|H||Hardcopy||Outputs to the printer, can be a single line, a range or the entire listing. For example;
|I||Insert||Inserts lines. You can specify a startline and an increment. For example;
|L||Loads from cassette.||Loads the first available file, unless a name is specified. For example;
|LD||Loads from disk.||Of course this only works if you are using Disk Edtasm|
|LDA||Loads from disk and appends||to the current edit buffer's contents.|
|M||Move||Same as copy except the original lines are deleted.|
|N||Renumber||Can specify a startline and the increment. For example;
|O||Displays available memory||Disk Edtasm only.|
|P||Prints a line or range of lines on the screen.||Similiar to Basic's LIST command.
|Q||Exits to Basic|
|R||Replace.||Replaces startline, can specify an increment also|
|T||Hardcopy No line numbers||Same as H command, except no line numbers are printed. I have no idea why anyone would want to do this.|
|V||Verify||Checks your cassette tape file for errors. Can specify a filename, for example;
|W||Writes to cassette.||Can specify a filename|
|WD||Writes to disk.||Can specify a filename|
|Z||ZBUG||Starts the ZBUG debugger|
3. The Assembler
This is the easy part, the computer does all the work for a change. You will appreciate this if you have ever done any hand coding. Once your source program has been edited to your satisfaction, start the assembler from the * prompt (Editor). The most common assembler command I use is A/IM/WE
|/AO||Absolute origin||Use this to force the assembler to locate the object code in a specific place.|
|/IM||In memory||Object code is assembled into memory|
|/LP||Line printer||Listing is printed out|
|/MO||Manual origin||Another method to locate the object code|
|/NL||No listing||No listing to screen|
|/NO||No object||No object code output|
|/NS||No symbol table||No symbol table listed|
|/SR||Single record||Never used this one, don't know what it is.|
|/SS||Short screen listing||Makes the listing slightly different|
|/WE||Wait on errors||Stops the assembly at any line with an error.|
|/WS||With symbols||Self explanatory|
If you have a short program to assemble, the A/IM/WE will work fine. If your program gets large, watching the listing go by on the screen seems to take forever. I usually use A/IM/WE/NL/NS to speed up the assembly. You are looking for 0000 errors at the end of listing. If your program has a lot of symbols, and the /WE switch is not on, you may not see the error count, so either turn on the /NS switch or include the /WE switch. Starting a program that has errors in it is a sure way to crash your computer. If you have errors, go back, edit the listing, and reassemble. Edtasm helps you here as it shows the lines with the error and tells you the type of error.
4. The debugger ZBUG
You have an error free listing, it is safe (maybe) to run the program. From the Editor's * prompt, type Z to enter ZBUG. The program will switch to a # prompt.
The most common command is G, the Go command. Type in G and the name of the symbol where your program starts. I always label my programs start as START, so my start command is always GSTART.
Likely your program will need some work, so this is where the debugger comes in. See the following list of commands.
|A||ASCII||Set examination mode to ASCII output|
|B||Byte||Set examination mode to Byte output|
|C||Continue||Restarts execution of your program after a breakpoint has stopped it.|
|D||Display||Shows all breakpoints that have been set.|
|E||Editor||Exits Zbug and returns you to the Editor|
|G||Go||The program is started at this program line
|H||Half Symbolic||Set display mode to half symbolic|
|I||Set the input base.||Can be 8, 10 (decimal), 16 (hexadecimal)|
|L||(Cartridge Edtasm) Load||Loads machine code from tape. Can specify a filename|
|LC||(Disk Edtasm) Load||Loads machine code from tape. Can specify a filename|
|LD||(Disk Edtasm) Load||Loads machine code from disk. Can specify a name and a loading offset if required.|
|LDS||(Disk Edtasm) Load||Loads machine code and the appended symbol table. Can specify filename, and load offsets for the code and the symbol table.|
|N||Numeric||Set display mode to Numeric|
|O||Set the output base.||Can be 8, 10 (decimal), 16 (hexadecimal)|
|P||(Cartridge Edtasm) Save||Saves machine code to tape. Specify start address, end address, and execution start address|
|PC||(Disk Edtasm) Save||Saves machine code to tape. Specify start address, end address, and execution start address|
|PD||(Disk Edtasm) Save||Saves machine code or memory to disk. Specify start address, end address, and execution start address|
|PDS||(Disk Edtasm) Save||Saves machine code to disk and appends the symbol table Specify start address, end address, and execution address.|
|R||Registers Displays the contents of all registers.||You usually use this right after a breakpoint when debugging.|
|S||Symbolic||Set display mode to Symbolic|
|T||Display||Shows contents of memory on screen. Must specify a start and end address.|
|TH||Print memory to printer.||Must specify a start and end address.|
|U||Copies memory.||Must specify a source address, destination address, number of bytes|
|X||Set breakpoint.||Must specify an address.(hard way) Just specify a symbol(easy way)|
|Y||Yank breakpoint.||If you specify an address it removes that breakpoint. By itself it removes all breakpoints.|
The Zbug Calculator
You will notice that Zbug displays its findings in hex. You can change this by typing I or O to change the input or display modes. A I10 command will set the input to base 10 decimal. If you want to set it back to hex, I16 will do it. To get the calculator to perform a decimal to hex conversion, type;
I10 O16 65535=
In this example I want to see what 65535 is in hex, Zbug will output FFFF.
To perform a hex to decimal conversion, the command is;
The calculator has a fair range of available operators
|+||Addition or positive|
|-||Subtraction or negative|
The best thing about Zbug's calculator is it will operate with not only numbers in any base, but also with symbols and ASCII characters. It only operates on whole numbers (integers), so don't try to do any math that will have anything to the right of the decimal point.
Out of time for now, will load more here ASAP. For now see the following sample;
Start your editor and enter the following
*I 00100 START JSR 43304 CLS SUBROUTINE 00110 LDA #65 ASCII A 00120 AGAIN JSR  CHROUT SUBROUTINE 00130 INCA NEXT IN ALPHABET 00140 CMPA #91 ONE PAST ASCII Z? 00150 BNE AGAIN 00160 LDA #32 ALPHABET DONE 00170 LDB #6 PRINT 6 SPACES 00180 REPEAT JSR  00190 DECB 00200 BNE REPEAT 00210 LOOP BRA LOOP 00210 END <break>
program assembles, must be 0 errors!
Your screen will clear, the alphabet will print at the top of the screen, and then Edtasm will break the program and return you to ZBUG.