WACOM Intuos 3

WACOM Intuos series is the high-end product line of WACOM tablets. Compared to Graphire or earlier Bamboo products, the circuit design is beefed-up in many aspects:

• Dedicated X and Y axis locating ASICs, makes it possible to perform X and Y axis locating simultaneously.
• Dedicated TX coils, makes it possible to achieve much larger active area. Infact the Intuos 3 PTZ-1231W have the largest active area of all WACOM tablets (excluding tablet display products). Also the transmit power is significantly higher than the previous products.
• Quadrature Heterodyne Downconversion, gives significantly better signal quality.
• More powerful ADC and DSP

The early Intuos series uses W6005S as the analog front end ASIC. Checkout the WACOM W6005S page for more information. I believe this AFE is later integrated into their all-in-one ASICs.

Theory of Operation

Please check the locating document for a general overview of the pen position detection mechanism shared by most EMR tablets. The following section will focus on the pen-to-tablet data communication.

Compared to the previous products, the Intuos 3 series uses a coherent FM demodulation scheme to achieve better noise immunity.

Data Link

Pen-to-Tablet Communication

Similar to the Graphire series, the Intuos series uses a fully-digital OOK data link. Curiously, the Intuos 3 series no longer uses an ASIC for the pen, but instead uses a microcontroller from the TI MSP430 family to do the CDC conversion and data transmission.

The pen seems to has three or more types of payload: Identification, Serial Number, and Running

Identification Mode (Mode 11)

The pen is in ID mode shortly after it's first in proximity to the tablet, and the pen sends a series of bits to identify itself.

From the captured data above, the 13-bit ID of the eraser and the pen tip differs only by 1 bit.

Known IDs:

ID	Accessory	Model Number
0011101111100	Grip Pen Tip	ZP-501E-00A
0010101111100	Grip Pen Eraser	ZP-501E-00A
0011011101100	Airbrush Tip	ZP-400E-00A
0010011101100	Airbrush Eraser	ZP-400E-00A
0001011111110	Mouse	ZC-100-02

Serial Number Mode (Mode 01)

After two frames of ID data, the pen sends the serial number once.

The middle part is the accessory ID, as can be seen in the About->Diagnose menu in the WACOM Tablet Properties control panel. The rest of the bits are unknown for now, probably accessory type (pen/eraser/mouse), checksum, etc.

What I know so far is the tip and eraser of the same pen have the same serial number payload.

Running Mode (Mode 00)

In the running mode, the pen sends the pressure data and key states to the tablet. Once identified, the pen seems to never go back to the ID mode until the pen is removed from the proximity of the tablet.

What I know so far is the tip and eraser of the same pen have the same running mode payload.

Alt Running Mode (Mode 10)

Some accessories, such as the Airbrush, have an additional mode that sends the wheel data.

Tablet-to-Pen Communication

Encoding

The tablet drives the coils with a fixed frequency OOK pulse. The duration of the drive signal is used to transmit data from the tablet to the pen.

The last two pulse of each data frame causes the pen to change its mode in the next data frame. When the pulse duration is very long, the accessory will reset itself. However, the exact duration is unknown and need some experimentation to find out.

Encoded Bit	Duration (us)
0	212.5
1	44
Accessory Reset	?

TX Power Control

When the pen is not captured by the tablet, the transmitter will switch to a high power mode to increase the range of the signal.

Known Models

• Intuos 3 Series
• PTZ-430 (A6 Size)
• PTZ-630 (A5 Size)
• PTZ-631W (A5 Height, but wide screen aspect ratio)
• PTZ-930 (A4 Size)
• PTZ-1230 (A3 Size)
• PTZ-1231W (A3 Height, wide screen. The largest tablet ever made !!)

References

• EP0967566A2, Figure 27, this document also have a general description of the digital data link used in the Intuos 3 series.
• JP4773315B2, Describes the protocol