UEXT
Encyclopedia
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
, SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
. The connector layout was specified by Olimex Ltd and declared an open-project that is royalty-free.
Physical characteristics
The UEXT connector consisting of 10 pins, in a two row by five male pin configuration, with a plastic keyed-shroud. All pins have a spacing of 0.1 inch (2.54 mm). The socket is mated with a 2x5 (10-pin) IDCInsulation-displacement connector
An Insulation-displacement connector, insulation-displacement technology/termination or insulation-piercing connector is an electrical connector designed to be connected to the conductor of an insulated wire or cable by a connection process which forces a selectively sharpened blade or blades...
female connector, and typically connected to a Ribbon cable
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 the resemblance of the cable to a piece of ribbon.Ribbon cables are usually seen for internal peripherals in computers, such as...
. The UEXT cable assembly is referred to as a 10-pin IDC Connector Ribbon Cable. These cables are readily available and cheap.
Electrical characteristics
I²C
I²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
, SPI
Serial Peripheral Interface Bus
The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
. All pins conform to 3.3 volt digital logic. The asynchronous serial bus requires additional level-shifting circuits and connectors to support RS-232
RS-232
In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
, RS-422, RS-485, DMX512, MIDI.
| Pin | Name | I/O | Logic | Primary Use |
|---|---|---|---|---|
| 1 | 3.3V | S | S | +3.3 volt Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... |
| 2 | GND | S | S | Ground |
| 3 | TXD | O | PP | Transmit Data for Async Serial bus |
| 4 | RXD | I | PP | Receive Data for Async Serial bus |
| 5 | SCL | O | OD | Clock for I2C bus |
| 6 | SDA | I/O | OD | Bidirectional Serial Data for I2C bus |
| 7 | MISO | I | PP | Serial Data In for SPI bus |
| 8 | MOSI | O | PP | Serial Data Out for SPI bus |
| 9 | SCK | O | PP | Clock Clock signal In electronics and especially synchronous digital circuits, a clock signal is a particular type of signal that oscillates between a high and a low state and is utilized like a metronome to coordinate actions of circuits... for SPI bus |
| 10 | SSEL | O | PP | Slave Select Chip select Chip select or slave select is the name of a control line in digital electronics used to select one chip out of several connected to the same computer bus usually utilizing the three-state logic.... for SPI bus |
Notes:
- Direction is relative to host board. I = Input, O = Output.
- S = Power SupplyIC power supply pinAlmost all integrated circuits have at least two pins that connect to the power rails of the circuit in which they are installed. These are known as the IC's power supply pins...
, PP = Push-Pull logic, OD = Open-DrainOpen collectorAn open collector is a common type of output found on many integrated circuits . Instead of outputting a signal of a specific voltage or current, the output signal is applied to the base of an internal NPN transistor whose collector is externalized on a pin of the IC. The emitter of the...
logic, all pins conform to 3.3 volt digital logic
Alternate Pin Uses
The functionality of most microcontroller 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 design considerations should be considered 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.
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
Resettable fuse
A polymeric positive temperature coefficient device is a passive electronic component used to protect against overcurrent faults in electronic circuits...
might be added between the host power and pin 1 to protect against over-current conditions.
Similar connectors
Some devices use a layout based on the UEXT connector but have chosen not 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.See also
- IDCInsulation-displacement connectorAn Insulation-displacement connector, insulation-displacement technology/termination or insulation-piercing connector is an electrical connector designed to be connected to the conductor of an insulated wire or cable by a connection process which forces a selectively sharpened blade or blades...
connector and Ribbon CableRibbon cableA 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 the resemblance of the cable to a piece of ribbon.Ribbon cables are usually seen for internal peripherals in computers, such as...
. - Asynchronous serial bus, using a UARTUniversal asynchronous receiver/transmitterA universal asynchronous receiver/transmitter, abbreviated UART , is a type of "asynchronous receiver/transmitter", a piece of computer hardware that translates data between parallel and serial forms. UARTs are commonly used in conjunction with communication standards such as EIA RS-232, RS-422 or...
, such as RS-232RS-232In telecommunications, RS-232 is the traditional name for a series of standards for serial binary single-ended data and control signals connecting between a DTE and a DCE . It is commonly used in computer serial ports...
and RS-422. - I2CI²CI²C is a multi-master serial single-ended computer bus invented by Philips that is used to attach low-speed peripherals to a motherboard, embedded system, cellphone, or other electronic device. Since the mid 1990s, several competitors I²C ("i-squared cee" or "i-two cee"; Inter-Integrated Circuit;...
serial bus, also known as "2-wire" bus. - SPISerial Peripheral Interface BusThe Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...
serial bus.