A serial mouse is designed to connect to a PC's true serial port - it's an actual RS-232 device using ±5V. As such it won't connect directly to the Arduino's RX/TX pins, you'll have to go through an RS-232 transceiver chip.

It also gets its power from the RTS line, but I never knew what the current draw of one of those things was - be careful trying to power it from the Arduino!

The actual protocol is a series of packets sent at 9,600 bps (8N1): from memory the early ones issued 5 data bytes then a line end:

• The first two bytes were the X-delta;
• The second two bytes were the Y-delta;
• The fifth byte was the different button states (one bit for each);
• Then an <LF> (hex 0x0A)?

I'll look up my old reference books...

Edit:

• Some quick Googling told me that the original protocol bears no resemblance to my memories: http://paulbourke.net/dataformats/serialmouse/
• And here's a page that describes a couple of other protocols: the last is much closer to my memory (albeit at 1,200 bps): http://www.cpcwiki.eu/index.php/Serial_RS232_Mouse

A serial mouse is designed to connect to a PC's true serial port - it's an actual RS-232 device using ±5V. As such it won't connect directly to the Arduino's RX/TX pins, you'll have to go through an RS-232 transceiver chip.

It also gets its power from the RTS line, but I never knew what the current draw of one of those things was - be careful trying to power it from the Arduino!

Different mouse manufacturers used different protocols. The original standard used a three-byte protocol at 1,200 bps 7N1. The encoding had the following properties:

• The leading bit of the first byte of the packet was set - all future bytes had the leading bit cleared.
• The first byte had the buttons' states, and the most significant bits of the X and Y deltas;
• The X delta was encoded in the second byte;
• The Y delta was encoded in the third byte.

http://paulbourke.net/dataformats/serialmouse/

Other manufacturers added things like extra buttons and scroll wheels that didn't fit in the packet structure. So they modified the protocol, but stuck with some features of the original:

• The data rate was (usually) still 1,200 bps, although sometimes they used 7N2 or 8N1 instead.
• The leading bit was still used to indicate start of packet;
• The X, Y (and Z) wheels still indicated deltas.

http://www.cpcwiki.eu/index.php/Serial_RS232_Mouse

A serial mouse is designed to connect to a PC's true serial port - it's an actual RS-232 device using ±5V. As such it won't connect directly to the Arduino's RX/TX pins, you'll have to go through an RS-232 transceiver chip.

It also gets its power from the RTS line, but I never knew what the current draw of one of those things was - be careful trying to power it from the Arduino!

The actual protocol is a series of packets sent at 9,600 bps (8N1): from memory the early ones issued 5 data bytes then a line end:

• The first two bytes were the X-delta;
• The second two bytes were the Y-delta;
• The fifth byte was the different button states (one bit for each);
• Then an <LF> (hex 0x0A)?

I'll look up my old reference books...

A serial mouse is designed to connect to a PC's true serial port - it's an actual RS-232 device using ±5V. As such it won't connect directly to the Arduino's RX/TX pins, you'll have to go through an RS-232 transceiver chip.

It also gets its power from the RTS line, but I never knew what the current draw of one of those things was - be careful trying to power it from the Arduino!

The actual protocol is a series of packets sent at 9,600 bps (8N1): from memory the early ones issued 5 data bytes then a line end:

• The first two bytes were the X-delta;
• The second two bytes were the Y-delta;
• The fifth byte was the different button states (one bit for each);
• Then an <LF> (hex 0x0A)?

I'll look up my old reference books...

Edit:

• Some quick Googling told me that the original protocol bears no resemblance to my memories: http://paulbourke.net/dataformats/serialmouse/
• And here's a page that describes a couple of other protocols: the last is much closer to my memory (albeit at 1,200 bps): http://www.cpcwiki.eu/index.php/Serial_RS232_Mouse