PS/2 Compatible Mouse Driver

The Basic Functions of the PS/2 Compatible Mouse Driver:

The PS/2 interface is a port on IBM and other computers for connecting keyboards and mice. It has been a standard interface for many years, although USB ports are now more common.

A few keyboards and mice have the option to connect to both USB and PS/2 ports through a passive wiring adapter. The adapter selects the correct connection type at power-on.

Stream Mode:

Stream mode allows a PS/2 mouse to communicate with a computer via the PS/2 port without having to install special hardware. In this mode, the mouse uses data packets to transmit X- and Y-movement counters in 9-bit 2’s complement notation (range -256 to +255) along with button state information.

During movement, the mouse sends data to the host in the form of 3-byte packets each containing the relative amount of X and Y motion since the last transmission. Each packet also includes a status byte that consists of 9-bit quantity values and an overflow indicator.

The data received by the mouse from a Stream Mode packet is processed and sent back to the host in an “echoing” mode. If the byte represents a valid command. It is answered by 0xFA which means that the mouse acknowledges that it has received the command.

Wrap Mode:

Wrap Mode is a way to test the connection between your mouse and your host. When it is entered the mouse sends a single data packet. And resets its movement counters. It is useful for testing the connection between the host and your mouse and can be used with all PS/2 compatible mice.

The first byte has a bunch of bit flags. And the second and third bytes contain deltaX and deltaY values in 9-bit two’s complement notation (typically a value of 1 for very slow movement, and 20 for very fast). These can be useful for measuring how far your cursor is from one point on the screen to another.

The bottom 3 bits of the first byte indicate whether the middle, right, or left mouse button is currently being held down. If the bit is set then it means that the button is being held down, otherwise, it means that it is not.

Reset Mode:

Reset Mode is a function that the PS/2 Compatible Mouse Driver performs when it’s connected to a PS/2 keyboard port. This function resets the mouse’s movement counters, so it can send data packets to the host.

The data packets are sent in a standard PS/2 protocol format. And they include movement counters in a 9-bit 2’s complement integer format. These counters are updated when the mouse reads its input and finds that movement has occurred. And they’re stored in Byte 1 of the movement data packet.

Other USB mouse drivers use different data reporting formats. This is because some mouse devices support additional features, such as buttons.

For these reasons, you may want to try installing a third-party program that will scan the web for available drivers and download and install them automatically for you. This will allow you to update your mouse’s drivers quickly without having to go through the tedious task of updating them yourself manually.

Data Reporting:

Data reporting allows the computer to send movement and button-position data to the mouse. The mouse decodes this information and uses it to perform actions on the user’s inputs.

This interface was first developed in IBM’s PS/2 computers in the 1980s and remains widely supported for backward compatibility. However, it’s losing ground to USB, which is the preferred interface for newer machines.

The PS/2 mouse interface uses a bidirectional serial protocol to transmit movement. And button-position data to the computer’s auxiliary device controller (keyboard controller). This controller then sends a series of commands to the mouse. Such as setting the report rate, and resolution, or resetting the mouse.

A “packet” may consist of a 3-byte movement data packet. A 2-byte completion-code-ID packet (see “Status Request” command), or a 1-byte response to a command. If the host receives an invalid packet. It may issue a “Resend” command, inhibit communication, or cycle the mouse’s power supply to reset the mouse.