40 lines
1.2 KiB
C#
40 lines
1.2 KiB
C#
using System;
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namespace BizHawk.Emulation.Computers.Commodore64.MOS
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{
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public class LatchedPort
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{
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public byte Direction;
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public byte Latch;
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public LatchedPort()
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{
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Direction = 0x00;
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Latch = 0x00;
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}
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// data works like this in these types of systems:
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//
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// directionA directionB result
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// 0 0 1
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// 1 0 latchA
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// 0 1 latchB
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// 1 1 latchA && latchB
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//
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// however because this uses transistor logic, there are cases where wired-ands
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// cause the pull-up resistors not to be enough to keep the bus bit set to 1 when
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// both the direction and latch are 1 (the keyboard and joystick port 2 can do this.)
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// the class does not handle this case as it must be handled differently in every occurrence.
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public byte ReadInput(byte bus)
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{
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return (byte)((Latch & Direction) | ((Direction ^ 0xFF) & bus));
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}
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public byte ReadOutput()
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{
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return (byte)((Latch & Direction) | (Direction ^ 0xFF));
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}
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}
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}
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