The quadrature encoder lines send square wave trains to the Mac that change with the velocity and direction of the mouse.
Mac emulator ps2 2017 plus#
The Plus mouse is a dumb device with five wires connected to it: one to the mouse button, and four others connected to rotary quadrature encoders for the mouse ball (two for the X axis and two for the Y axis). The Mac Plus mouse operates differently from a PS2 mouse. A delta of 1 unit in X or Y represents a physical movement of about 1/4 of a millimeter.Ĭhapter 10 of the book FPGA Prototyping by Verilog Examples is entirely devoted to the development of a PS2 mouse interface, freeing me from the need to write one myself. The mouse only reports these movement deltas, not its current position in absolute terms. This packet contains the current state of the left, middle, and right mouse buttons, as well as two 9-bit signed values indicating how far the mouse has moved in X and Y since the last packet.
Mac emulator ps2 2017 update#
Once the mouse enters stream mode, it will send a 3-byte update packet to the computer whenever the mouse position or button state change.
The mouse acknowledges the command by sending the byte $FE. The first thing the computer must do is send the mouse a command instructing it to enter “stream mode”, which is accomplished by sending the command byte $F4. When power is first applied, the mouse enters a passive state.
Mac emulator ps2 2017 serial#
The details of arbitrating control of the clock and data lines to determine the direction of a transfer make the interface more complex than a one-way serial connection, but there are many good examples found online that explain the process well. PS2 MouseĪ standard PS2 mouse uses a bidirectional serial interface to communicate with the computer. Perhaps a future version of the Plus Too might add USB input support with a microcontroller serving as a USB host, but for now PS2 is it.
They also require a 5V power supply, whereas everything else in the Plus Too will run at 3.3V. The downside of PS2 input devices is that they’re growing less common, having been mostly replaced with USB devices now. I plan to use a PS2-type keyboard and mouse, since they both communicate with a fairly simple serial protocol that’s easy to work with.
Digging further into the Plus Too design details, the next systems to consider are the keyboard and mouse.
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