GPIO Service

This service can check the 8 GPIO Pins (A0, A1, A2, A3, A4, A5, D6, D7).

Check the Pinout page to locate this Pins in the Pinout of the UDOO BLU.

They can work as:

• Digital Pins in Input or Output mode.
• PWM Output signal.
• Analog Input voltage data (Only the Pins: A0, A1, A2, A3, A4, A5)

User can manage these functions by the following characteristics:

Pin Mode

exposes a Value attribute composed by an unsigned integer 16 bits long. It's logically divided in 8 2-bit pairs. Each pair represents the pin operating mode.

The following tables shows respectively the mapping of bit pairs of each pin, and the different operation modes.

Pin	Bit Pair
A0	0:1
A1	2:3
A2	4:5
A3	6:7
A4	8:9
A5	10:11
D6	12:13
D7	14:15

Pair Value	Pin Mode
00	Digital Output
01	Digital Input
10	Analog
11	PWM

For example, to set the pin D6 in PWM mode, you will need to write in the characteristic value 0x0300.

Digital Data

Exposes Value attribute composed by an 8-bit unsigned int.
Each bit represents the pin status:

• 0 LOW (GND)
• 1 HIGH (VDD).

The write operation is performed only when the corresponding pin is set as Digital Output (see Pin Mode).
The read operation, on the other hand, is always possible, but the value of each bit is meaningful only if the corresponding pin is in Digital Input or Digital Output mode.
In Digital Input mode "floating" pins are read as 1.

The diagram below shows the mapping of the physical pin on the bits of the value of this feature:

Bit (position)	Pin
0	A0
1	A1
2	A2
3	A3
4	A4
5	A5
6	D6
7	D7

Client Configuration Characteristic: this descriptor is used to activate notifications for Digital Data characteristic. The notification is sent when a pin changes its state, and sends the entire Value attribute of Digital Data. The time interval specified in the characteristic Notifind Period is ignored.

Analog Read

Allows the user to read an analog value of a pin. The pin to be read is selected by the Index characteristic (see below). The Value attribute is two bytes long, but only the last 12 bits are significant and provide the ADC data.

Characteristic Client Configuration: see description in Common Characteristics and Notes.

Index

This value is an unsigned 8 bits integer field used to indicate which pin will be used in the next operation.
Allowed values from 0 to 7 (corresponding to the pin A0, A1, A2, A3, A4, A5, D6, D7) or 0xFF, but, as indicated in the table below, not all values are allowed for both operations. It is used to read all analog pin in sequence if set to 0xFF.
Each reading it is increased automatically, from 0 to 5.
A further reading returns the index to 0, allowing a new cycle on all pins. If Pin Mode is different from 10 (Analog mode) it will return the value 0. It should be noted that, since the operation of Analog Read and PWM Config occurs subsequently to writing Index, UDOO BLU verifies only that the value Index falls within {0-7, FF}. If operation is requested later with an Index value not legal, it is silently ignored.

Operation	Proper Index Value
Analog Read	0, 1, 2, 3, 4, 5, FF
PWM Config	0, 1, 2, 3, 4, 5, 6, 7

PWM Config

this characteristic is composed by two fields:

• Frequency: is an 32 bits unsigned integer field used to set the PWM signal frequency (Hz). It can vary from a minimum of 3 to a maximum of 24000000 (24 MHz). PWM signal starts immediately after the value is written. Writing 0 interrupt the signal.
• Duty cycle: is an 8-bit unsigned integer field that is used to set the fraction of the period in which the PWM signal is high. It's percentage and vary between 0 and 100. It should be noted that the signal resolution is limited by the timer length, which is equal to 24 bits. For higher frequencies, frequency and duty cycle will be rounded to the nearest binary value. For example, a signal at 24 MHz may have 0% duty cycle only, 50% or 100%.

Notifind Period: see description in Common Characteristics and Notes; the value is significant only when reading Analog pin.