Difference between revisions of "Input"
From SizeCoding
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jnz mainloop ;fall through if 0, do jump somewhere else if otherwise | jnz mainloop ;fall through if 0, do jump somewhere else if otherwise | ||
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| + | Sometimes your <code>AH</code> register does not contain <code>00h</code> at any given time. In that case <code>dec ax</code> will never trigger the zero flag, so you would have to spend the extra byte and use <code>dec al</code>. Alternatively you can redesign your codeflow as to have <code>00h</code> in <code>AH</code> at least sometimes ;) | ||
== Checking for '''any''' keypress == | == Checking for '''any''' keypress == | ||
Revision as of 08:14, 14 August 2016
Checking for ESCAPE
This is fairly easy: Monitor the keyboard scancode port for ESC which is #1, then deal with it:
in al,60h ;read whatever is at keyboard port; looking for ESC which is #1
dec ax ;if ESC, AX now 0
jnz mainloop ;fall through if 0, do jump somewhere else if otherwise
Sometimes your AH register does not contain 00h at any given time. In that case dec ax will never trigger the zero flag, so you would have to spend the extra byte and use dec al. Alternatively you can redesign your codeflow as to have 00h in AH at least sometimes ;)
Checking for any keypress
If you need to shave a byte, it might be possible in some environments to check for any keypress instead of just escape using less code:
in al,60h ;read whatever is at keyboard port
das ;If non-zero, parity will be set
jp mainloop ;Jump if parity
An alternative if not running DOSBox:
in al,60h ;read whatever is at keyboard port
aaa
jz mainloop ;Jump if zero
The above are somewhat flaky due to different hardware, VMs, and emulators not honoring flags correctly.
