Universal EXTension (UEXT) is a connector layout which includes power and three serial buses:

Asynchronous Asynchrony is any dynamic far from synchronization. If and as parts of an asynchronous system become more synchronized, those parts or even the whole system can be said to be in sync. Asynchrony or asynchronous may refer to: Electronics and com ...

, I²C, and SPI separately over 10

pins A pin is a device, typically pointed, used for fastening objects or fabrics together. Pins can have the following sorts of body: *a shaft of a rigid inflexible material meant to be inserted in a slot, groove, or hole (as with pivots, hinges, an ...

in a 2×5 layout. The connector layout was specified by Olimex Ltd and declared an open-project that is

royalty-free Royalty-free (RF) material subject to copyright or other intellectual property rights may be used without the need to pay royalties or license fees for each use, per each copy or volume sold or some time period of use or sales. Computer standards ...

in 2011, and was used in all their boards after 2004.

Physical characteristics

The UEXT connector consists of 10 pins, in a two row by five male pin configuration, with a plastic keyed- shrouded or box header (specifically BH10S). All pins have a spacing of 0.1 inch (2.54 mm). The socket is mated with a 2×5 (10-pin) IDC female connector, and typically connected to a

ribbon cable A ribbon cable is a cable with many conducting wires running parallel to each other on the same flat plane. As a result, the cable is wide and flat. Its name comes from its resemblance to a piece of ribbon. Ribbon cables are usually seen fo ...

. The UEXT cable assembly is referred to as a ''10-pin IDC Connector Ribbon Cable''. These cables are readily available and cheap.

Electrical characteristics

The UEXT connector presents power and three serial buses:

, I²C, SPI. All pins conform to 3.3 volt digital logic. The asynchronous serial bus requires additional level-shifting circuits and connectors to support

RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

RS-422 RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance, first issued in 1975, that specifies the electrical characteristics of a digital signaling circuit. It was meant to be the foundation ...

RS-485 RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and Telecomm ...

DMX512 DMX512 is a technical standard, standard for digital communication networks that are commonly used to control lighting and effects. It was originally intended as a standardized method for controlling stage lighting dimmers, which, prior to D ...

, or

MIDI Musical Instrument Digital Interface (; MIDI) is an American-Japanese technical standard that describes a communication protocol, digital interface, and electrical connectors that connect a wide variety of electronic musical instruments, ...

. Notes: # Direction is relative to host board. I = Input, O = Output. # S =

Power Supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, electric current, current, and frequency to power ...

, PP = Push-Pull logic, OD =

Open-Drain Open collector, open drain, open emitter, and open source refer to integrated circuit (IC) output pin configurations that process the IC's internal function through a transistor with an exposed terminal that is internally unconnected (i.e. "open ...

logic, all pins conform to 3.3 volt digital logic

Alternate pin uses

The functionality of most

microcontroller A microcontroller (MC, uC, or μC) or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable input/output peripherals. Pro ...

pins are multipurpose, thus allowing the engineer to redefine the purpose of the pin. It is fairly common that a pin will have a choice to be either a general purpose I/O or a peripheral. If a microcontroller pin is connected to the UEXT connector and redefined to be something other than Asynchronous Serial Bus / I²C Bus / SPI Bus, then some thought should be given to the design before making the changes. To minimize the chance of damaging various UEXT boards or the microcontroller, redefined pins should continue to adhere to the direction of the data in this table or alternately redefined as an input. For a safe design, it is recommended that you don't redefine pins 4 or 7 to be outputs, and use pin 6 as an output with caution.

User concerns

If a person is concerned about damaging the data lines of the microcontroller, additional over-voltage protection diodes and/or separate drivers should be added between the microcontroller and UEXT connector. Additionally, a

resettable fuse A resettable fuse or polymeric positive temperature coefficient device (PPTC) is a passive electronic component used to protect against overcurrent faults in electronic circuits. The device is also known as a multifuse or polyfuse or polyswit ...

might be added between the host power and pin 1 to protect against over-current conditions. Open source UART dongles are available that are explicitly designed to be pin compatible with UEXT, and may be used to interface a UEXT device directly with a computer over USB.

5 V warning

Some boards might provide 5 V output on UEXT pins if they are configured for operation at 5V. For example, OLIMEXINO-328 and OLIMEXINO-32U4 have a 3.3 V/5 V PTH jumper that changes the power mode of the board. If the 3.3 V/5 V jumper is set to 5 V, this jumper also changes the voltage available at pin #1 of UEXT as well as the voltage levels of all data signals available there (UART, SPI, I2C). As the UEXT standard only defines 3.3 V, many UEXT modules may not be 5 V tolerant, and thus get damaged if the board has such jumper set to 5V. Users are advised to verify their boards are configured for 3.3 V before connecting UEXT hardware to prevent damaging said hardware.

Parallel cables

It is possible to connect multiple UEXT devices in parallel by clamping additional IDC connectors onto the same ribbon cable. This will result in a correct distribution of power (3.3 V and ground) and allow data communication over I²C. However, a multidrop SPI bus will fail since all the chip selects are tied together, thus all peripherals will be addressed simultaneously resulting in their simultaneous response data on the MISO line being scrambled. UART will also fail due to multiple devices transmitting and receiving on the same lines. Series resistors are necessary on conflicting SPI and UART pins to limit short circuit currents due to conflicts, if compatibility with other UEXT devices is desired.

Similar connectors

Some devices use a layout based on the UEXT connector but have chosen not to implement all of the functionality. In particular the asynchronous serial connection may have been omitted. In these cases the spare pins are usually assigned other purposes, such as connecting to a device reset line, so care should be taken to check the exact connector layout on the schematic of a particular device.

Implementations

;UEXT I/O Boards
Olimex UEXT Boards
;Host Boards
Olimex Olimexino-328
16 MHz ATMEGA328 (

Atmel AVR AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. They are 8-bit RISC single-chip microcontrollers based on a modified Harvard architecture. AVR was one of the first microcontroller ...

)
Olimex Olimexino-STM32
72 MHz STM32F103RBT6 (

ARM Cortex-M3 The ARM Cortex-M is a group of 32-bit reduced instruction set computer, RISC ARM architecture, ARM processor cores licensed by Arm (company), ARM Limited. These cores are optimized for low-cost and energy-efficient integrated circuits, which h ...

)
Olimex LPC-P1114
50 MHz NXP LPC1114 (

ARM Cortex-M0 The ARM Cortex-M is a group of 32-bit RISC ARM processor cores licensed by ARM Limited. These cores are optimized for low-cost and energy-efficient integrated circuits, which have been embedded in tens of billions of consumer devices. Thoug ...

)
Olimex DuinoMite
80 MHz MicroChip PIC32MX795 ( PIC32)
Olimex STM32-P207
120 MHz ST STM32F207 (

) * Olimex Pinguino ;3rd-party * LibreSolar

References

External links

UEXT connector webpage

UEXT specification

OLIMEX Ltd
{{Portalbar, Electronics Electrical signal connectors