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C64 BASIC: How to suppress the '?' sign when using the INPUT command?
Accepted answer
32 votes

Use the INPUT# command. The INPUT# command is meant for non-interactive I/O on files or devices, i.e. reading from a file on disk, serial port, whatever. Because it is non-interactive, it will not ...

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Why does the 6502 have the BIT instruction?
23 votes

A good example would be reading from the floppy drive on the C64. The incoming clock and data signals of the serial bus are (perhaps not accidentally) wired to bits 6 and 7 of port A on CIA#2, ...

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How can I implement the modulus operator in Commodore 64 Basic?
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19 votes

Using this expression A-INT(A/B)*B

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Under what circumstances would RAM locations 0 and 1 be written and/or read on the C64?
Accepted answer
18 votes

Data lines hold their previous state if nothing drives them Each trace on the motherboard has some tiny capacitance, depending on its length, routing, and distance from the ground plane. Each time ...

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What was computer "Fuzzy" logic?
17 votes

I came across Motorola HC12 and Hitachi SH2 series controllers in the 90s, intended for vehicle engine control units, that had some fuzzy logic capability. Motorola had some new machine code ...

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Is DOS being shipped with or as an installed OS?
17 votes

As of today, the German price comparison website idealo.de lists 11 PC systems and 91 laptops that come with FreeDOS preinstalled, mainly from MSI, Lenovo, HP and ASUS. Not only cheap entry level ...

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Sprites not rendering correctly before $2000
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16 votes

Yes, there is a limitation. Due to incomplete address decoding, the VIC sees the bitmap font ROM between $1000 and $1FFF and $9000-$9FFF. Here is the end of the font ROM (the C64/chargen file in VICE)...

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When does the VIC-II read the sprite data?
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16 votes

There are 63 to 65 clock cycles in a scanline, depending on the VIC model (PAL, old/new NTSC). Each cycle consists of two phases, the 6510 is only able to access memory in the high phase, the VIC-II ...

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6510 I/O port initialisation
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15 votes

Yes, your assumption is correct. Like in any microcontroller design I know of, I/O lines with programmable direction are set to input on reset. The 6510 is no exception, its data direction register ...

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Graphics chips in 1980
14 votes

The Motorola MC6847, used in the TRS-80 Color Computer, or the Texas Instruments TMS9918 would be good candidates. Both were available in 1980, and could display 256x192 pixel colour images.

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Obscure uses of the Commodore 8050/1541 disk drive
12 votes

Playing music with the drive heads, of course. I've tried that too, wrecking the drive in the process. Dimming the drive LED, by flashing it very fast, with a variable duty cycle. Printing a file on ...

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How were files transferred between different systems in the late 1980s?
11 votes

There were (and are) a few possibilities to transfer programs* and data between 8 bit Commodore systems and other platforms via floppy disks and other media. Commodore 1541 floppy drives could be ...

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How was C ported to architectures that had no hardware stack?
6 votes

A program stack is a very simple data structure that requires only indexed or indirect memory addressing (pointers) indirect or computed jumps a designated register or global variable holding the ...

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Was self-modifying code possible using BASIC?
5 votes

Program code as data file Microsoft Basic, e.g. on 8 bit Commodore machines, supported reading and writing program files on floppy disk like sequential data files. OPEN 2,8,2,"EXAMPLE,P,W" would ...

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Why do the i8080 I/O instructions take a byte-sized operand to determine the port?
5 votes

The port number can take 256 possible operands. Apparently d8 means an 8-bit operand. From the 8080 Assembly Programming Manual The OUT instruction has a similar description. Seeing this line IN ...

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Why does Sinclair BASIC have two formats for storing numbers in the same structure?
4 votes

Doing integer arithmetic is by some orders of magnitude faster as floating point. So if there is a statement like LET a = b + c the interpreter would first check if both a and b are integers. If yes,...

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What happened to the Apple Device SBC that was supposed to compete with the linux SBCs?
3 votes

It is an April Fool's Day article. https://hackaday.com/ 2016/04/01 /apple-introduces-their-answer-to-the-raspberry-pi/

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Reading data over serial from an old punched tape reader
1 votes

I'd first double-check that the switches are correctly set, then try looking for flow control issues. If software flow control is selected (DC Codes and SW3 are ON), the reader waits for a DC1 (XON, ...

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