A Quickie Introduction to the Windows Based 68K Assembler EASy68K

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Neil Gaines
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1 A Quickie Introduction to the Windows Based 68K Assembler EASy68K You now have a number of options to assemble your code for your microcontroller. One option, of course, is to assemble it by hand, using the byte by byte machine codes from the programmer s reference. Ouch. This might prove to be a little bit painful for you, though, so some thoughtful and generous people have given of their time and made available assemblers that will make your job far easier. The most basic of these may be the dos command line assembler described in another document on your class website. However, for those of you who don t like being all command-line-y and would prefer something more windows like, another program called EASy-68K may be more your speed. It s available for free download off the course website or several others and is provided to the world under the gnu public license, so feel free to install it on your home system if you d like to play with it there, too. Here s a quickie intro to get you started. From the start menu on any of the lab computers, open: Start:Programs:EASy68K:Edit68k. It will give you a blank template. As a starter, let s enter the test program from last week s lab. It s about as humble as programs can possibly be. Enter the following code: * Program : A basic loop program * Written by : Joseph Bloe * Date : 3/14/16 (Pi Day, 2016) * Description: A most basic program to use the editor START ORG $100 LOOP nop bra.s LOOP END START When you re done, your screen should look like below:

2 Save it, then, time to simulate. Go to Project:Assemble Source. This brings up the simulator. It should look similar to below.

This verifies your program assembly code from last week. Notice your memory locations, along with the machine code, offsets, etc. all nicely calculated for you along the left side.

3 This verifies your program assembly code from last week. Notice your memory locations, along with the machine code, offsets, etc. all nicely calculated for you along the left side. If you run it, you ll see it loops just like you saw with your microcontroller last week. Here s a little more complicated example. A little more but not much Go back to the editor, start a new file and enter the following code: * Program : A basic loop program * Written by : Joseph Bloe * Date : 3/14/16 (Pi Day, 2016) * Description: A most basic program to use the editor START ORG $1000 LOOP move.w #$1000,D0 move.w D0,D1 add.w #$0003,D0 bra.s LOOP END START Your screen should look like this at this point:

This program is also brainlessly simple. Put an immediate value in D0, move D0 to D1 using register direct addressing. Add an immediate value to D0 And go back to LOOP.

4 This program is also brainlessly simple. Put an immediate value in D0, move D0 to D1 using register direct addressing. Add an immediate value to D0 And go back to LOOP. Again, save and simulate, giving the following screen: Notice you have all sorts of goodies to help you debug. You can see, most importantly for us: The Program Counter Data Registers Address Registers Status Registers Cycle Counts

5 Step through the program by clicking the Trace into button (6 th button from the left with the straight right arrow). You ll go step by step through the program. Notice a few things. -- The registers (data, address, program counter, etc) update as you step through the program. -- The cycles counter changes, but not by the same amount for each instruction. Different opcodes require different numbers of cycles to execute. Also, the blue line represents the current location of the program counter. Reset the simulation by clicking the Reset Program button. Start stepping through the program. When does the D0 register get updated? What is the Program counter value? The registers are always a step behind the program counter -- One final point: Your peripherals are primarily going to be memory mapped I/O devices. The 68K controllers don t differentiate between memory and I/O space. So, one of the easiest ways for your to watch outputs is simply to watch the memory locations assigned to them. Do this using the memory utility View-Memory. Always keep in mind, however, what your hardware is doing. In our case, remember, for example, that as of lab 19 address $8000 is mapped to both the keypad output AND the displays. So you much keep this in mind if you use a memory map to view input or output. The hardware simulator portion of the assembler may be of use as well, but if you use it do so with some caution. Be sure you understand how each of the parts works. The LED displays, for example, are true 7 Segment LED s, with an 8 th bit as the decimal point. Here s a short program you can play with to experiment with how they work. Set your display address to $E000 and $F000 respectively. Enter it and try running it if you like. * Program : 7 Segment Example with Rotate * Written by : Joseph Bloe * Date : 3/14/16 (Pi Day, 2016) * Description: A most basic program to use the editor START ORG $1000 * 7 Segment and LED Array Example move.b #$0001,D0 LOOP move.b D0,$E000 move.b D0,$F000 ROL.b #1,D0 bra.s LOOP * You should see the LEDS and march across the screen to the left * and around the 7 segment display * Since there's no pause, you should AutoTrace to slowly step * through the program. END START

6 Here s the hardware display. Again, be sure the addresses match what you expect in your coding. The 7 segment displays do not, you ll note have the fancy decoding chip, latches, etc that your displays for your address bus do. So while $FF will display as FF on your data or address displays, it will display as 8. on these displays. Hardware is king be sure you know what yours is doing. If you look at the memory map, the values should of course, correspond. There are many more things you can do with the simulator. See the help file for more details. But this will get you started doing assembly programs.

Physics 116B Winter 2006: Problem Assignment 8

Physics 116B Winter 2006: Problem Assignment 8 Due Wednesday, March 15 1. You may use a calculator for the following: (a) Convert to decimal: $9F03. (b) Express in binary: $3CFA. (c) Convert to hexadecimal: