Everything about the Commodore 128, or the C128, or the CBM128. It featured BASIC 7.0. I never had one, but my friend Frank did – complete with Modem and 80 column monitor. Buy did we have fun dialling up those BBSes after school.
The Commodore 128 was marketed as being “three computers in one”. I guess technically they were correct when they made that statement. Although I’m very find of the native 128 mode, the system saw its uses mostly as a games machines in C64 mode. I don’t recall anybody ever looking at CP/M mode longer than half an hour (if that).
There are three ways to put the C128 into C64 mode. Two of which I always knew about, ever since my friend Frank Jagow bought himself a whole C128 system from his paper route money in 1986. But the third option’ve only recently learnt about – after over 30 years of being a C128 fanboy. How exciting!
In this screencast I’ll show you how to write your own INPUT routine in Commodore BASIC. This comes in handy when you want to reject certain keys from being used when asking users for keyboard input. In my example I’m going to allow all alpha characters (A-Z), as well as SPACE, RETURN and the DELETE key.
In this episode I’ll show you how to create the iconic flashing borders on Commodore machines. Back in the day, when the system was loading, this was a nice way to indicate that the computer is busy doing something rather than being dead.
I’ll show you the principle both in BASIC and in Machine Language on the C128. The VIC-II chip is the same on the C64 though, so this will also work on the Commodore 64.
The same approach can be used on the Plus/4, however the addresses for the border and background colours are different (decimal 65305, or hex $FF19).
In this episode I’ll explain the concept of Flow Control in Commodore BASIC. It’s kind of a video update of a post I did a while ago.
In essence, it means that we can tell the programme to take a different route in the code depending on a condition that’s met. We’ll explore the IF/THEN and ON… GOTO/GOSUB statements (available on all versions of Commodore BASIC), as well as the expanded IF/THEN/ELSE version (available on the C128 and Plus/4 only).
In addition, I’ll also show you how to use the BEGIN and BEND clauses that were introduced with the C128.
The Commodore 128 has a built-in machine language monitor which makes it ideal for ML development. However, most (or pretty much all) documentation on this subject is geared towards the Commodore 64, making it slightly difficult to get a head start in writing ML code for the 128.
Before I forget how to do it, here are a few pointers – courtesy of Jim Butterfield’s book “Machine Language – Expanded Edition”.
Let’s begin by typing MONITOR in C128 mode. It’ll take us to the machine language monitor. We’ll start our programme at $0B00. To begin assembling our code, we’ll type A 0B00 (A for Assemble), followed by these lines:
The MONITOR will turn this text into the output you’ll see in the screenshot above (the lines starting with a . dot). Here’s what this code will do when called:
First we’ll load the X register with a value of zero. We’ll use this register as a counter. In the next line we’ll load the accumulator with whatever is stored in address $0C10 plus whatever is stored in the X register. So if X has a value of zero, then the contents of $0C10 will be loaded. If X was 1, then the value in $0C11 would be loaded, and so forth.
We’re using this as ASCII representation of our text (Hello World in a box in this case). With JSR $FFD2 we’ll call a Kernal routine that prints a single character onto the screen. Now we’re incrementing X by one and ask if it’s 45 yet (CPX #$2D). This would indicate that we’ve printed all the characters we need. If that’s not the case, we’ll return to line 2 and keep printing. Otherwise, we’ll stop the programme.
Storing ASCII characters
You’d think it was possible to simply type in text in the MONITOR. But of course that would be too easy. Instead we need to grab one of those massive tables and hack in each character’s ASCII code in hex. How convenient!
Type M 0C10 (or whichever location in memory you’d like to store your text string at) and overtype the numbers at the start of the line, each one representing a single byte of our ASCII text. At the end of each line you’ll see what those characters look like when converted.
In my case it’s a total of 45 characters, beginning with a return, followed by the top of the box, HELLO WORLD, and the bottom of the box.
Running from the MONITOR
To start the programme from the monitor, we’ll type G F0B00. We’ll end up with a SYNTAX ERROR and back on the BASIC screen though due to the RTS command at the end of the listing. If we replace it with a BRK command instead, we’ll end up back in the MONITOR.
The important thing to remember is the five digit addressing mode on the C128 (i.e. G for GO, followed by F0B00). Our programme starts at $0B00 in memory, but to make it run properly we’ll have to specify which BANK it should be called from. Anything other than BANK 0 or BANK 1 is fine, otherwise we won’t reach the print routine at $FFD2. In my example I’m choosing F, but E would work fine too (as we’ll see in a moment).
Running from BASIC
Type X to exit the monitor and go back into the land of BASIC. First we’ll need to choose a BANK. We’ll have 16 to choose from (0 to 15), so perhaps let’s try BANK 15. Now we’ll need to type the start of our programme in decimal:
or we can use the DEC command to convert hex to decimal on the fly:
Saving the programme
From the MONITOR, we can save the programme using the S command. It needs to be followed by a name (in double quotes), followed by the drive number, memory start and memory end plus one byte – all separated by a comma. It’s probably easier to show than to write:
We’re saving more bytes than strictly necessary here due to the large gap between our code and the beginning of the ASCII string. Our string could go up to $0C3F. The last byte in $0C40 is NOT saved to disk (or tape).
We can do the same from BASIC using the BSAVE command (for Binary SAVE). The syntax is BSAVE “FILE NAME”, P1234 TO P5678. Sadly the DEC command doesn’t work inline with this command, which would make it extremely useful. We’ll have to convert the values into decimal manually instead.
Loading the programme
To bring our masterpiece back into the computer from the MONITOR, the L command works a treat:
From BASIC we can load the programme the usual way, making sure we load it with ,DEVICE,1 at the end. This is to make sure it is loaded into the same memory it was saved from, rather than the start of BASIC:
In this episode I’m adding statistics support to my previous lottery generator on the Commodore 64.
I’ll add an array that is updated if my supplied numbers have been matched, and how many times over how many draws this has happened. I’ll also add an option to pause the programme and display the statistics before random draws can continue.
When this app is run continuously it will collect statistical data on how many lottery draws are necessary to match all supplied numbers.
PS: By the time the video had uploaded, my emulator had drawn over one million sets, and none of them have matched my numbers 🙁
In this episode I’m amending my previous lottery number generator to take six lucky numbers from the user to match against the randomly drawn numbers from the Commodore 64.
This will allow us to compare what the computer has drawn to the user’s input, as well as keep drawing numbers until the user input comes up. It’ll be an interesting experiment to see how many draws that will take…
In this episode I’m demonstrating how to print numbers in evenly spaced columns in Commodore BASIC.
On the C128 and the Plus/4 we can use a nifty little function called PRINT USING for this, with which we can format the output of any printed text or variable.
On the C64 and VIC-20 that function doesn’t exist, so we’ll have to convert a numeric value into a string (using the STR$ function), and then determine how long our string is. Following that we’ll have to manually pad our string value with as many spaces as are required. Continue reading How to print numbers as columns in Commodore BASIC→