Matrix Orbital Corp

Hi,

I need to use GTT480272A using I2C communication with a microcontroller. For sending commands to the touchscreen, the microcontroller acts as Master for I2C communication. But when a touch response is detected on the touchscreen, the display sends the received touch response to the microcontroller. So, how does the microcontroller (Master) comes to know that touchscreen (Slave) is sending some data.

Can the slave initiate a start signal on the I2C bus? I need to understand the implementation of I2C communication between my microcontroller and display.

Is it the case that, microcontroller has to be slave whenever it is not sending any command and waiting for touch response? But again in this case, the display need to know the slave address of microcontroller for I2C communications.... I did not got any information on this in the hardware manual or the protocol manual.... Please reply ASAP...

Thanks in advance...

Hi Pads,

I see you're working with the GTT in the newest released protocol: I2C. Your understanding of the protocol is good; the host controller will always be the master and the display always the slave.

Unfortunately, this means that the display cannot provide an immediate signal to the controller when a touch event occurs. The host controller will have to periodically read from the display to determine what touch, or other, events have occurred.

~Troy

Hi,

Thanks for your response.

I have following questions?

1) Host controller initiates an I2C transaction by addressing slave screen (80) and make device to send data by coding R/W bit of the address byte appropriately. If the touch response is received, the slave sends return prefix (252), the touch designator 135, length, event type, and finally the region index where the event occurred. Is my understanding correct?

2) If the touch response is not received, what data does slave send to the host controller on periodically reading? This information is required for host controller to understand that no touch response is received.

3) Does GTT480272 operate in I2C mode at standard mode (100kbps) or at fast mode (400kbps) ?

Waiting for your response

Thanks in advance.

Clark wrote:Hi Pads,

I see you're working with the GTT in the newest released protocol: I2C. Your understanding of the protocol is good; the host controller will always be the master and the display always the slave.

Unfortunately, this means that the display cannot provide an immediate signal to the controller when a touch event occurs. The host controller will have to periodically read from the display to determine what touch, or other, events have occurred.

~Troy

No worries Pads,

I'm sure I can provide a little more info on the GTT480272A-I2C

1) You are correct, the display (slave) will place each touch event in its output buffer waiting to be read by the host.

2) As documented in the manual, "read until an unexpected zero is received." Unfortunately, no NAK is provided but it is possible to determine the expected length of all responses.

3) Again, in the I2C Communication section of the manual, "The GTT can communicate as fast as 400kbps."

Thanks,
~Troy