Expand 18 Click

How does it work?

Expand 18 Click is based on the PCAL9714, an ultra low-voltage translating 14-bit SPI I/O expander from NXP. This board enables I/O expansion for a wide range of microcontroller (MCU) families, offering additional GPIO (General Purpose Input/Output) pins with minimal interconnection requirements. It operates via the SPI interface, making it compatible with various MCUs. Its ultra-low voltage interface supports direct communication with MCUs operating at voltages as low as 1.1V, while simultaneously interfacing with I/O devices at different voltage levels. This I/O expanding solution is particularly suited for tasks that require interfacing with sensors, push buttons, keypads, and other input devices, all while ensuring that power consumption and pin usage are kept to a minimum.

The PCAL9714 used in Expand 18 Click features an integrated level-shifting capability, providing exceptional flexibility in systems with mixed power supplies. It operates with two distinct power supplies: one for its logic side and one for its core circuits. The logic side can be powered by either the 3.3V or 5V mikroBUS™ power rails, selectable via the VCC SEL jumper. The core circuits, however, can draw power either from the 3.3V mikroBUS™ rail or an external power source connected to the VEXT pins, supporting voltages from 1.65V to 5V. This core circuit power source is adjustable via the VDDP SEL jumper, ensuring optimal voltage management for diverse application needs.

Expand 18 Click communicates with the host MCU via a 4-wire SPI interface, supporting a maximum clock frequency of 5MHz, ensuring efficient and reliable data transfer. In addition to the SPI interface, the board includes an active-low RST pin to reset the PCAL9714 in case of time-outs or operational issues. The power-on reset restores the registers to their default state and reinitializes the SPI state machine, while the RST pin allows the same reset process without requiring a complete power cycle.

The PCAL9714 also incorporates Agile I/O features, enhancing the functionality of the I/Os. These features include programmable output drive strength, latchable inputs, programmable pull-up and pull-down resistors, maskable interrupts, an interrupt status register, and configurable open-drain or push-pull outputs. Additionally, Agile I/O Plus offers interrupts specified by level or edge, with the ability to clear them individually without affecting other events. The interrupt (INT) pin is triggered when an input state changes from its corresponding Input Port register state, alerting the host MCU of the change.

At power-on, all I/Os are configured as inputs. However, the host MCU can easily reconfigure them as either inputs or outputs by writing to the appropriate I/O configuration bits. Data for each I/O is stored in the corresponding input or output register, and the Input Port register’s polarity can be inverted through the Polarity Inversion register, eliminating the need for external logic gates. Programmable pull-up and pull-down resistors further reduce the need for discrete components.

The expander outputs offer 25mA sink capabilities, allowing for direct LED driving while maintaining low current consumption. Additionally, the PCAL9714 features a hardware pin for SPI-bus address programming, accessible via the ADDR SEL jumper, enabling up to four devices to share the same SPI bus.

This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.

Specifications

Pinout diagram

This table shows how the pinout on Expand 18 Click corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
	NC	1	AN	PWM	16	NC
Reset / ID SEL	RST	2	RST	INT	15	INT	Interrupt
SPI Select / ID COMM	CS	3	CS	RX	14	NC
SPI Clock	SCK	4	SCK	TX	13	NC
SPI Data OUT	SDO	5	MISO	SCL	12	NC
SPI Data IN	SDI	6	MOSI	SDA	11	NC
Power Supply	3.3V	7	3.3V	5V	10	5V	Power Supply
Ground	GND	8	GND	GND	9	GND	Ground

Onboard settings and indicators

Expand 18 Click electrical specifications

Software Support

We provide a library for the Expand 18 Click as well as a demo application (example), developed using MIKROE compilers. The demo can run on all the main MIKROE development boards.

Package can be downloaded/installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on MIKROE github account.

Library Description

This library contains API for Expand 18 Click driver.

Key functions

• expand18_set_pin_direction This function sets the direction of the selected pins.

• expand18_set_all_pins_value This function sets the value of all output pins.

• expand18_read_port_value This function reads the value of the selected port input pins.

Example Description

This example demonstrates the use of Expand 18 Click by setting and reading the ports state.

void application_task ( void ) 
 { 
     uint8_t port_value = 0; 
     for ( uint16_t pin_num = EXPAND18_PIN_0_MASK; pin_num <= EXPAND18_PIN_7_MASK; pin_num <<= 1 ) 
     { 
         expand18_set_all_pins_value( &expand18, pin_num ); 

         expand18_read_port_value( &expand18, EXPAND18_PORT_0, &port_value ); 
         log_printf( &logger, " Status port 0 (output): 0x%.2Xrn", ( uint16_t ) port_value ); 

         expand18_read_port_value( &expand18, EXPAND18_PORT_1, &port_value ); 
         log_printf( &logger, " Status port 1 (input) : 0x%.2Xrnn", ( uint16_t ) port_value ); 
         Delay_ms( 1000 ); 
     } 
 }

The full application code, and ready to use projects can be installed directly from NECTO Studio Package Manager (recommended), downloaded from our LibStock™ or found on MIKROE github account.

Other MIKROE Libraries used in the example:

• MikroSDK.Board
• MikroSDK.Log
• Click.Expand18

Additional notes and informations

Depending on the development board you are using, you may need USB UART click, USB UART 2 Click or RS232 Click to connect to your PC, for development systems with no UART to USB interface available on the board. UART terminal is available in all MIKROE compilers.

mikroSDK

This Click board™ is supported with mikroSDK – MIKROE Software Development Kit. To ensure proper operation of mikroSDK compliant Click board™ demo applications, mikroSDK should be downloaded from the LibStock and installed for the compiler you are using.

For more information about mikroSDK, visit the official page.