Microbit 硬件架构介绍

文章来至http://tech.microbit.org/hardware/

Microbit Shop

这篇内容为近期整理介绍，我们尽可能维持正确性，若有发现错误，请参考 GitHub here上的数据为左证参考

概述

Overview 概述
Getting Started With the micro:bit Hardware 如何开始使用microbit
Hardware Description 硬件构造及零件说明
- nRF51 Application Processor 蓝芽主要IC
- Bluetooth Wireless Communication 蓝芽通讯描述
- Low Level Radio Communications 无线通信描述(同样用2.4Ghz ，但不是用蓝芽通讯协议)
- Buttons 按键
- Display 显示屏
- Accelerometer 重力传感器
- Magnetometer 磁力传感器
- Temperature Sensing 温度感测
- General Purpose Input/Output Pins 数字输入出
- Power Supply 电力供应
- Interface 接口IC 说明
- USB Communications USB 通讯
- Debugging 除错
- Mechanical 机构
Links 相关连结

如何开始使用microbit 硬件

Microbit 硬件设计是根据ARM mbed技术所开发的应用IC及相干周边功能所设计出来的! 另外有一颗接口IC 用来处理USB 接口及拖拉式核心软件更新法.这接口IC 并未用来链接任何周边.

两部分关键信息可以一窥Microbit 的内部设计:

线路图(schematics), 可以看到主要零件的链接方式及设计.
参考设计及相关模块数据(reference design), 这部分的数据可以帮助进一步了解Microbit 的设计及变动性

硬件相关说明

nRF51 应用处理器IC

nRF51 应用处理器IC是让使用者作主要程控的处理器，完整的程序包含了用户客制及中介层(runtime) 及蓝芽协议层(Stack)，(译者注:浏览器编译环境会在用户程序写完同时，将这三部分整合完成) 一旦用户将完整程序(HEX 文件)放在USB 闪存根目录上，处理器便会直接执行程序代码。使用者也可对连接在这处理器上的GPIO去做控制. 也可透过 2.4GHz 无线去做相关周边的控制.

项目	说明
Model	Nordic nRF51822-QFAA-R rev 3
Core variant	ARM Cortex-M0 32 bit processor
Flash ROM	256KB
RAM	16KB
Speed	16MHz
Debug	SWD, jlink/OB
More Info	here

蓝芽通讯

板子上2.4G无线相关设计提供了对手机平板的蓝芽通讯功能

项目	说明
Stack	Bluetooth 4.1 with Bluetooth low energy
Band	2.4GHz ISM (Industrial, Scientific and Medical) 2.4GHz..2.41GHz
Channels	50 2MHz channels, only 40 used (0 to 39), 3 advertising channels (37,38,39)
Sensitivity	-93dBm in Bluetooth low energy mode
Tx Power	-20dBM to 4dBm in 4 dB steps
Role	GAP Peripheral
Congestion avoidance	Adaptive Frequency Hopping
Profiles	1 BBC micro:bit profile
More Info	here

无线通信

板子上2.4G无线相关设计提供另外的无线通信协议（Nordic Gazell），这通讯协议已经在不同的程序语言环境可以直接使用，并且可以在多个microbit 装置中互相传递并且群组化（group code ）.

项目	说明
Protocol	Nordic Gazell
Freq band	2.4GHz
Channel rate	1Mbps or 2Mbps
Encryption	None
Channels	101 (0..100)
Group codes	255
Tx power	Eight user configurable settings from 0(-30dbm) to 7 (+4dbm)
Payload size	32 (standard) 255 (if reconfigured)
More Info	here

按键

Microbit 正面有两个按钮，背面有一个。背面的按键连接至KL26 接口ＩＣ及 nRF51 处理器做系统重制用(reset)

正面的按键A 、 B 是可以由使用者去做程控包括了短压、长压或是A、B同时按，按键A、B 均连接至金手指（edge connector）上的GPIO ，加上电路设计可以做logic 0 或 1值的操作.

项目	说明
Type	2 tactile user buttons, 1 tactile system button
Debounce	(A & B) software debounced, 54ms period
Pullup	(A & B) external 4K7, (System) 10K

显示

在板子上有5x5 数组LEDs.做为显示屏，microbit 是以3x9 数组电路去控制它.并用很高的速度去刷新它。以下暂不翻译但保留（ LED matrix is also used to sense ambient light, by repeatedly switching some of the LED drive pins into inputs and sampling the voltage decay time, which is roughly proportional to ambient light levels.）

项目	说明
Type	minature surface mount red LED
Physical structure	5x5 matrix
Electrical structure	3x9
Intensity control	10 steps
Intensity range	TBC
Sensing	ambient light estimation via software algorithm
Sensing Range	TBC, 10 levels from off to full on
Colour sensitivity	red centric, red is 700nm

重力传感器（加速度传感器）

重力传感器是经由I2C 跟处理器连结，并提供了三轴的感应数据并包含了手势感测的算法 (like : fall detection, logo-up, logo-down, shake)

项目	说明
Model	Freescale MMA8653FC
Features	3 axis, 2/4/8g ranges
Resolution	10 bits (0..1023)
Max output data rate	800Hz
On board gestures	‘freefall’
Other gestures	Other gestures are implemented by software algorithms in the runtime.

磁力传感器

磁力传感器也是透过I2C 跟处理器连结，提供了磁力感测数值，并提供指南针功能，（The compass must be calibrated before use, and the calibration process is automatically initiated by the runtime software – 译者对这段有些疑虑，暂不翻译）

项目	说明
Model	Freescale MAG3110
Max update rate	80Hz
Full Scale range	1000uT
Sensitivity	0.10uT

温度感测

nRF51 处理器提供了板子上的实时温度感测(Run time ambient temperature sensing ).

项目	说明
Type	on-core nRF51
Sensing range	-25C .. 75C
Resolution	0.25C steps
Accuracy	+/-4C (uncalibrated)
More Info	here

数字输入输出(GPIO)

金手指 (edge connector) 上有许多 GPIO 。处理器上有许多的多任务讯号针脚(pin define) ，有些已经设定成GPIO 功能连接至金手指，如何进一步使用这些针脚请参阅 (nRF51 data sheet)

项目	说明
Rings	3 large IO rings and two large power rings, 4mm plug and crocodile clip compatible
GPIO features	19 assignable GPIO pins
	2 are assigned to the on board I2C interface
	6 are used for display or light sensing feature
	2 are used for on board button detection
	1 is reserved for an accessibility interface
	19 may be assigned as digital input or digital output
	19 may be assigned for up to 3 simultaneous PWM channels
	19 may be assigned for 1 serial transmit and 1 serial receive channel
	6 may be assigned as analog input pins
	3 may be assigned to an optional SPI communications interface
	3 may be assigned for up to 3 simultaneous touch sensing inputs
ADC resolution	10 bit (0..1023)
Edge Connector	Edge connector data sheet
Pitch	1.27mm, 80 way double sided.
Pads	5 pads, with 4mm holes
More Info	here

电力供应

给microbit的电力，主要是由接口IC透过USB 提供，亦可由电池盒连接器提供，在金手指上亦有电力供应的功能，需要熟悉电路设计的人操作.

项目	说明
Operating range	1.8V .. 3.6V
USB current	120mA max
Onboard Peripherals budget	30mA
Battery connector	JST X2B-PH-SM4-TB
Battery current	TBC
Max current provided via edge connector	90mA
More Info	here

界面

这接口IC提供USB链接功能、拖拉式程序刷新(drag and drop flash program)及跟主计算机做序列通讯(serial communication) .

项目	说明
Model	Freescale MKL26Z128VFM4
Core variant:	ARM Cortex-M0+
Flash ROM	32KB
RAM	4KB
Speed	16MHz
Debug capabilities	SWD
More Info	here

USB通讯

主要意思跟上一段雷同，不做翻译但保留原文(The micro:bit has an on board USB communications stack, that is built into the firmware of the interface chip. This stack provides the ability to drag and drop files onto the MICROBIT drive in order to load code into the application processor. It also allows serial data to be streamed to and from the micro:bit application processor over USB to an external host computer, and supports the CMSIS-DAP protocol for host debugging of application programs.)

项目	说明
Connector	USB micro, MOLEX_47346-0001
USB version	1.1 Full Speed device
Speed	12Mbit/sec
USB classes supported	Mass Storage Class (MSC)
	Communications Device Class (CDC)
More Info	here

除错

译者尚未做过这段的实务操作所以暂不翻译先保留原文(The interface processor can be used with special host tools to debug code that is running on the application processor. It connects to the application processor via 4 signal wires. The KL26 interface processor code can also be debuged via it’s integral SWD software debug interface, for example to load initial bootloader code into this processor at manufacturing time, or to recover a lost bootloader.)

项目	说明
Protocol	CMSIS-DAP
Options	JLink/OB (via different firmware)
More Info	here

机构

我们有提供2D 跟3D CAD 图文件，这些资料可以用来提供microbit 营销及项目资料甚至3D printing 的生产制造的图文件数据.

项目	说明
Dimensions	5cm(w) 4cm(h)
Weight	5g

Micro:bit 中文台灣中國