How to access keyboard directly trough I/O ports (in DOS)?

Question

I'm writing a program for DOS and I want to get keyboard input. The thing is that I don't want to get that input using BIOS or DOS. What's the proper way to get keyboard input without using DOS or BIOS? I mean what's the way to get keyboard input in the lowest level of programming using I/O ports. Thanks!

@BasileStarynkevitch there isn't much info about this topic. — Arnas, Oct 22 '12 at 19:26
Check out [this answer](http://stackoverflow.com/a/10525397/968261). — Alexey Frunze, Oct 23 '12 at 02:42
@AlexeyFrunze thanks, but that's a little bit too hard for me I'd say. I need something easier... — Arnas, Oct 23 '12 at 10:59
@Arnas Come on, it's a tiny program. You will learn something from it. And that's the "proper way". — Alexey Frunze, Oct 23 '12 at 16:52
@AlexeyFrunze thank you! I've analyzed that program, I pretty much understand it now. Thanks again! — Arnas, Oct 23 '12 at 21:41

score 1 · Accepted Answer · answered Oct 22 '12 at 19:29

1

You need to do an inb instruction on port 0x60 to read the scancode from the keyboard.


static inline uint8_t inportb(uint16_t port)
{
    uint8_t ret;
    asm volatile ("inb %1, %0" : "=a" (ret) : "dN" (port));
    return ret;
}
scancode = inportb(0x60);

If you want to know when there's new input you need to setup an interrupt handler to listen for PS/2 interrupts or use USB polling depending on your keyboard.

answered Oct 22 '12 at 19:29

Jesus Ramos

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Hello, I tried to read port 60h port, but whenever I read it, it instantly returns 28 (scancode of ENTER key). It doesn't even let me to give any input. Maybe I need to clear a buffer? If so, could you please tell me how can I do that? – Arnas Oct 22 '12 at 21:23
@Arnas I believe that if you read from the data port on the keyboard it always contains the last key pressed (which is probably enter). Is it USB or PS/2 keyboard by any chance? – Jesus Ramos Oct 22 '12 at 23:10
The one I was using was USB, but I have another one with PS/2. – Arnas Oct 23 '12 at 10:31
For PS/2 you need to setup an interrupt handler for when new data is available. For USB you need to do some extra work which I am not so familiar with currently. – Jesus Ramos Oct 23 '12 at 18:12

How to access keyboard directly trough I/O ports (in DOS)?

1 Answers1