Touchscreen is used widely all over the world today. It is so easy to use that everyone even whoknows nothing about computers can use it.Meanwhile,It’s well known that Universal Serial Bus (USB)is a huge success,and USB-based peripherals are everywhere. Because of the two advantages,Thecombination of touchscreen and USB is a very good choice. So,We try to improve our designs toprovide the customers with more easy_to_ease touchscreen connections interface.
Touchscreen Controller Protocol
The
USB devices can be divided into several classes.The HID class consists
primarily of devices thatare used by humans to control the operations of
the computer systems. Our GeneralTouch touchscreenUSB interface is a
typical application of HID class. Its main function are as follows:
*. The HID firmware specification(version 1.1) is supported;
*.
Supports x,y and z touchscreen coordinate system, and they are absolute
touchscreen values;Itsrange is 0~4095 for x ,y coordinate system and
0~255 for z coordinate system.
*. Supports Left,Right,and Middle button modes, and you can change touchscreen button modes withSET_REPORT HID command;
*. Most HID commands are supported, GET_PROTOCOL and SET_PROTOCOL commands are notrequired, so they are not supported;
.Touch Packets Report Format
The touch packet is composed of ButtonState and X,Y, Z coordinates.Its total length in bytes in 7.
Byte0 Byte1 Byte2 Byte3 Byte4 Byte5 Byte6
Buttons XLow XHigh YLow YHigh ZLow ZHigh
Buttons = button state,see description below;
XLow = X touch coordinate low byte;
XHigh = X touch coordinate high byte;
YLow = Y touch coordinate low byte;
YHigh = Y touch coordinate high byte;
ZLow = Z touch coordinate low byte;
ZHigh = Z touch coordinate high byte;
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Reserved Reserved Reserved Reserved Reserved Middle Right Left
Left = Left button down flag,If 1,the left button is down;
Right = Right button down flag,If 1,the right button is down;
Middle = Middle button down flag,If 1,the middle button is down;
NOTES:The Reserved bits are defined as 0.
.Feature Report Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
Reserved Reserved Reserved Reserved Reserved Middle Right Left
Left = Left button mode flag,If 1,current button mode is Left button mode;
Right = Right button mode flag,If 1,current button mode is right button mode;
Middle = Middle button mode flag,If 1,current button mode is middle button mode;
Reserved = Reserved,defined as 0.
NOTES:Default button mode is Left button mode,Device driver writers can choose to use this
feature to provide the user with button mode support,Also,They can just choose to use their
drivers provide button mode emulation support.
.Appendix
1.) USB Touchscreen Device Descriptor
/* HID USB Touchscreen device descriptor */
const char device_desc_table[]=
{
0x12, /* size of descriptor (18 bytes) */
0x01, /* descriptor type (device descriptor) */
0x10, 0x01, /* USB spec release (ver 1.1) */
0x00, /* class code (each interface specifies class information) */
0x00, /* device sub-class (must be set to 0 because class code is 0) */
0x00, /* device protocol (no class specific protocol) */
0x08, /* maximum packet size (8 bytes) */
0xFC, 0x0D, /* vendor ID (vendor ID) */NOTES
0x01, 0x00, /* product ID (USB touchscreen product ID) */NOTES
0x01, 0x00, /* device release number */
0x01, /* index of manufacturer string (1) */
0x02, /* index of product string (2) */
0x00, /* index of serial number string (not supported = 0x00) */
0x01 /* number of configurations (1) */
};
NOTES:We have received our vendor ID from USB IF recently,It is decimal 3580 and hexadecimal
0DFC.So we modify this descriptor here.
2.) USB Touchscreen HID Report Descriptor
/* HID Touchscreen report descriptor */
const char hid_report_desc_table[]=
{
0x05, 0x01, // USAGE_PAGE (Generic Desktop)
0x09, 0x02, // USAGE (Mouse)
0xa1, 0x01, // COLLECTION (Application)
0x09, 0x01, // USAGE (Pointer)
0xa1, 0x00, // COLLECTION (Physical)
0x05, 0x09, // USAGE_PAGE (Button)
0x19, 0x01, // USAGE_MINIMUM (Button 1)
0x29, 0x03, // USAGE_MAXIMUM (Button 3)
0x15, 0x00, // LOGICAL_MINIMUM (0)
0x25, 0x01, // LOGICAL_MAXIMUM (1)
0x95, 0x03, // REPORT_COUNT (3)
0x75, 0x01, // REPORT_SIZE (1)
0x81, 0x02, // INPUT (Data,Var,Abs)
0x95, 0x01, // REPORT_COUNT (1)
0x75, 0x05, // REPORT_SIZE (5)
0x81, 0x03, // INPUT (Cnst,Var,Abs)
0x05, 0x01, // USAGE_PAGE (Generic Desktop)
0x09, 0x30, // USAGE (X)
0x09, 0x31, // USAGE (Y)
0x09, 0x00, // USAGE (Undefined)
0x15, 0x00, // LOGICAL_MINIMUM (0)
0x26, 0xFF,0x7F, // LOGICAL_MAXIMUM (32767)
0x35, 0x00, // PHYSICAL_MINIMUM(0)
0x47, 0xFF,0xFF,0x00,0x00, // PHYSICAL_MAXIMUM(65535)
0x75, 0x10, // REPORT_SIZE (16)
0x95, 0x03, // REPORT_COUNT (3)
0x81, 0x02, // INPUT (Data,Var,Abs)
0xc0, // END_COLLECTION
0xa1, 0x01, // COLLECTION (Application)
0x05, 0x09, // USAGE_PAGE (Button)
0x19, 0x01, // USAGE_MINIMUM (Button 1)
0x29, 0x03, // USAGE_MAXIMUM (Button 3)
0x15, 0x00, // LOGICAL_MINIMUM (0)
0x25, 0x01, // LOGICAL_MAXIMUM (1)
0x95, 0x03, // REPORT_COUNT (3)
0x75, 0x01, // REPORT_SIZE (1)
0xb1, 0x02, // FEATURE (Data,Var,Abs)
0x95, 0x01, // REPORT_COUNT (1)
0x75, 0x05, // REPORT_SIZE (5)
0xb1, 0x03, // FEATURE (Cnst,Var,Abs)
0xc0, // END_COLLECTION
0xc0 // END_COLLECTION
};
NOTES:We are sorry to say that we’ve changed our device’s HID descriptor.We list the revision
as follows:
1. Changed USAGE(Z) to USAGE(Undefined),because some platforms try to interpret this value
in the way which is not expected;
2. Changed LOGICAL_MINIMUM and LOGICAL_MAXIMUM,PHYSICAL_MINIMUM and
PHYSICAL_MAXIMUM range value for USAGE(X),USAGE(Y),USAGE(Undefined);
Any suggestions and comments are appreciated.
3.) USB Touchscreen EndPoint Descriptor
/* HID Touchscreen Endpoint descriptor */
const char Endpoint_Descriptor[]=
{
0x07, /* descriptor length (7 bytes) */
0x05, /* descriptor type (ENDPOINT) */
0x81, /* endpoint address (IN endpoint, endpoint 1) */
0x03, /* endpoint attributes (interrupt) */
0x07, 0x00, /* maximum packet size (7 bytes) */
0x0A /* polling interval (10ms) */
};
4.) USB Touchscreen Class Descriptor
/* HID Touchscreen HID descriptor */
const char Class_Descriptor[]=
{
0x09, /* descriptor size (9 bytes) */
0x21, /* descriptor type (HID) */
0x10, 0x01, /* class specification (1.10) */
0x00, /* hardware target country */
0x01, /* number of hid class desriptors to follow (1) */
0x22, /* report descriptor type (2) */
sizeof(hid_report_desc_table),
0x00
};
5.)USB Touchscreen Interface Descriptor
/* HID Touchscreen Interface descriptor */
const char Interface_Descriptor[]=
{
0x09, /* length of descriptor (9 bytes) */
0x04, /* descriptor type (INTERFACE) */
0x00, /* interface number (0) */
0x00, /* alternate setting (0) */
0x01, /* number of endpoints (1) */
0x03, /* interface class (3..defined by USB spec) */
0x01, /* interface sub-class (1..defined by USB spec) */
0x02, /* interface protocol (2..defined by USB spec) */
0x00 /* interface string index (not supported) */
};
6.)USB Touchscreen Configuration Descriptor
/* HID Touchscreen Configuration descriptor table */
const char config_desc_table[]=
{
0x09, /* length of descriptor (9 bytes) */
0x02, /* descriptor type (CONFIGURATION) */
0x22, 0x00, /* total length of descriptor (33 bytes) */
0x01, /* number of interfaces to configure (1) */
0x01, /* configuration value (1) */
0x04, /* configuration string index (4) */
0xE0, /* configuration attributes (self powered, remote wakeup) */
0x00 /* maximum power (set at 0,because it is self_powered.)*/
};
NOTES:We changed the configuration attributes and maximum power used by our device here,
We found that the USB bus can not provide enough power to our device,or if it can,the other
device on the device may be affected.
We changed our device to Self_Powered,that is,it does not consume any power from the bus now.