Plus/4 Archives

How to generate Lottery Numbers on the Commodore 64

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In this episode I’ll demonstrate how to draw random lottery numbers on a Commodore 64. The secret sauce here is not only the RND function to generate random numbers, but also two loops inside each other that prevent the same number from coming up more than once. Here’s the lottery generator code: 10 x=rnd(-ti) 20 … Read more

String Operations on Commodore Computers

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Commodore BASIC has some interesting and simple string functions built in. Three of them are self explanatory: LEN, LEFT$ and RIGHT$. But others, like the mysterious MID$ and INSTR functions, are a little tricker, and I can never remember how they works. So here’s a quick recap on how they all work. LEN (A$) Returns … Read more

How to play sounds and music on the Commodore Plus/4

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The Plus/4 has a total of two voices thanks to its integrated TED chip, which is also responsible for rendering text and graphics on screen. The first voice can play square waves, while the second one can generate either square wave sounds or white noise.

Let’s see how we can make him play a tune.

We can use some BASIC keywords to make the Plus/4 be all musical. First we need to turn up the volume by using the VOL command. We can set this to anything between 0 and 8.

VOL 8

Next we can use the SOUND command to make each channel play a note, like so:

SOUND 1,400,60

This will play a one-second long note on channel 1.

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How to use direct block access commands in Commodore DOS

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Commodore-Logo-PaddedWe can access each sector’s raw data on Commodore disk drives with direct block access commands. Supported drives include the 1541, 1571, the VICE emulator as well as the SD2IEC card reader (for the most part).

Each single sided floppy contains 35 sectors, while a double sided 1571 formatted disk contains 70 sectors. Each track contains between 17 and 21 sectors depending on how far inside or outside they are. Each sector contains 255 bytes we can read or write.

Sectors are the same as blocks: only the directory refers to them as “blocks” and shows us how many we have available.

We’ll need to open two channels to our disk drives: a command channel and a data channel. Here’s how to do it:

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How to split a long string into separate words in Commodore BASIC

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Here’s a quick word splitter routine for CBM BASIC. It takes phrase and “explodes” all words into an array, removing spaces. Feel free to adopt it for your own needs. 10 rem word splitter 20 rem splits a long phrase into words at a space 30 input “tell me something”;a$ 40 rem clear current array … Read more

Commodore Plus/4 Screen Memory Map (Display RAM)

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The Commodore Plus/4 – like his other brothers – has memory areas in which screen characters and colour values are stored independently from each other. Because it uses the TED chip these memory addresses are different from the C64 and C128. Each character from the top left corner to the bottom right corner occupies one … Read more

How to use SD2IEC: a quick command reference

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I’ve ordered an SD2IEC a few weeks ago from Nic over at http://sd2iec.co.uk. It’s an SD card reader for Commodre computers and emulates many features of the 1541 Floppy Disk Drive. I went for the Limited Edition made from authentic recycled C64 plastic – so this little critter used to be a real C64! This … Read more