概述

　　基站里不同的设备都有RS485对外接口，通讯接口有20Mbps和40Mbps两种不同速度，为了使各设备实现同步需要MCU从GNSS获取时钟，再通过RS485总线统一各设备时间一致性，同时把信息保存下来。为实现上述功能需要双串口高速的MCU以及带ESD保护功能的全双工RS485芯片。

　　优势

　　· Silicon Labs 8位MCU EFM8UB20，系统时钟速度可达48MHz，内部系统时钟精度±1.5%,内置64K Flash、4K XRAM，丰富的外设资源(两个UART、一个IIC、一个SPI、40个GPIO口)，TQPF48封装满足产品设计需求，-40℃到85℃工业级工作范围，两种供电方式可选，包括2.65V到 3.6 V供电或使用内部集成5V转3.3V LDO 5V供电。主推型号，性价比高。

【EFM8UB20】

EFM8UB属于Universal Bee系列MCU，为业界集成度最高、带USB接口的混合信号8位微控制器。EFM8UB2搭载高精度振荡器、时钟恢复电路以及集成收发器，不需要任何外部元件即可用于所有全速USB应用。

产品特色

流水线式8位8051 MCU内核，最大工作频率达48 MHz

兼容无晶振全速/低速USB 2.0的控制器，具有1kB缓冲区

一个单端差分10位ADC和两个模拟比较器

内部48MHz振荡器支持无晶振USB和UART操作，在使用USB时钟恢复时精度为±0.25%

2个UART、1个SPI、2个SMBus/I2C串行通信接口

EFM8UB20框图

EFM8 Universal Bee Family EFM8UB2 Data Sheet

The EFM8UB2, part of the Universal Bee family of MCUs, is a multi-purpose line of 8-bit microcontrollers with USB feature set.

These devices offer high value by integrating a USB peripheral interface with a high precision oscillator, clock recovery circuit, and integrated transceiver, making them ideal for any full speed USB applications with no external components required. With an efficient 8051 core and precision analog, the EFM8UB2 family is also optimal for embedded applications.

EFM8UB2 applications include the following:

• USB I/O controls, dongles

• High-speed communication bridge

• Consumer electronics

• Medical equipment

KEY FEATURES

• Pipelined 8-bit 8051 MCU Core with 48 MHz maximum operating frequency

• Up to 40 multifunction I/O pins

• Crystal-less full speed/low speed USB 2.0 compliant controller with 1 KB buffer memory

• One differential 10-bit ADC and two analog comparators

• Internal 48 MHz oscillator with ±0.25% accuracy with USB clock recovery supports crystal-free USB and UART operation

• 2 UARTs, SPI, 2 SMBus/I2C serial communications

Feature List

The EFM8UB2 highlighted features are listed below.

• Core:

• Pipelined CIP-51 Core

• Fully compatible with standard 8051 instruction set

• 70% of instructions execute in 1-2 clock cycles

• 48 MHz maximum operating frequency

• Memory:

• Up to 64 KB flash memory, in-system re-programmable from firmware.

• Up to 4352 bytes RAM (including 256 bytes standard 8051 RAM and 4096 bytes on-chip XRAM)

• Power:

• Internal LDO regulator for CPU core voltage

• Internal 5-to-3.3 V LDO allows direct connection to USB supply net

• Power-on reset circuit and brownout detectors

• I/O: Up to 40 total multifunction I/O pins:

• Flexible peripheral crossbar for peripheral routing

• 10 mA source, 25 mA sink allows direct drive of LEDs

• Clock Sources:

• Internal 48 MHz precision oscillator ( ±1.5% accuracy without USB clock recovery, ±0.25% accuracy with USB clock recovery)

• Internal 80 kHz low-frequency oscillator

• External crystal, RC, C, and CMOS clock options

• Timers/Counters and PWM:

• 5-channel Programmable Counter Array (PCA) supporting PWM, capture/compare, and frequency output modes with watchdog timer function

• 6 x 16-bit general-purpose timers

• Communications and Digital Peripherals:

• Universal Serial Bus (USB) Function Controller with eight

flexible endpoint pipes, integrated transceiver, and 1 KB

FIFO RAM

• 2 x UART

• SPI™ Master / Slave

• 2 x SMBus™/I2C™ Master / Slave

• External Memory Interface (EMIF)

• Analog:

• 10-Bit Analog-to-Digital Converter (ADC0)

• 2 x Low-current analog comparators

• On-Chip, Non-Intrusive Debugging

• Full memory and register inspection

• Four hardware breakpoints, single-stepping

• Pre-loaded USB bootloader

• Temperature range -40 to 85 ºC

• Single power supply 2.65 to 3.6 V

• QFP48, QFP32, and QFN32 packages

With on-chip power-on reset, voltage supply monitor, watchdog timer, and clock oscillator, the EFM8UB2 devices are truly standalone system-on-a-chip solutions. The flash memory is reprogrammable in-circuit, providing non-volatile data storage and allowing field upgrades of the firmware. The on-chip debugging interface (C2) allows non-intrusive (uses no on-chip resources), full speed, in-circuit debugging using the production MCU installed in the final application. This debug logic supports inspection and modification of memory and registers, setting breakpoints, single stepping, and run and halt commands. All analog and digital peripherals are fully functional while debugging. Each device is specified for 2.65 to 3.6 V operation and is available in 32-pin QFN, 32-pin QFP, or 48-pin QFP packages. All package options are lead-free and RoHS compliant.

　　· Intersil的RS485通讯芯片ISL3177E，供电范围3V到3.6V，总线上可接入256个设备，-40℃到85℃工业级工作范围，MSOP8和SOIC两种封装可供选用，支持热插拔。20Mbps全双工通讯，±15kV IEC61000标准 ESD 保护使通讯安全可靠。

【ISL3177E】

±15kV IEC ESD Protected, 3.3V, Full-duplex, 20Mbps RS-485/RS-422 Transceiver

Key Features

IEC61000 ESD protection on RS-485 I/O pins: ±15kV

Class 3 ESD Level on all other pins: >7kV HBM

Full fail-safe (open, short, terminated/floating) receivers

Hot plug - Tx and Rx outputs remain three-state during power-up (only versions with output enable pins)

True 1/8 unit load allows up to 256 devices on the bus

Single 3.3V supply

High data rates: up to 20Mbps

Low quiescent supply current: 800μA (Max)

Ultra low shutdown supply current: 10nA

-7V to +12V common mode input/output voltage range

Half and full duplex pinouts

Three state Rx and Tx outputs available

Current limiting and thermal shutdown for driver overload protection

Tiny MSOP packages consume 50% less board space

Pb-free (RoHS compliant)

Description

The Intersil ISL317xE are ±15kV IEC61000 ESD protected, 3.3V powered single transceivers that meet both the RS-485 and RS-422 standards for balanced communication. These devices have very low bus currents (+125mA/-100mA), so they present a true “1/8 unit load” to the RS-485 bus. This allows up to 256 transceivers on the network without violating the RS-485 specification’s 32 unit load maximum, and without using repeaters. For example, in a remote utility meter reading system, individual meter readings are routed to a concentrator using an RS-485 network, so the high allowed node count minimizes the number of repeaters required.

Receiver (Rx) inputs feature a “Full Fail-Safe” design, which ensures a logic high Rx output if Rx inputs are floating, shorted, or terminated but undriven.

Hot Plug circuitry ensures that the Tx and Rx outputs remain in a high impedance state while the power supply stabilizes.

The ISL3170E through ISL3175E utilize slew rate limited drivers which reduce EMI, and minimize reflections from improperly terminated transmission lines, or unterminated stubs in multidrop and multipoint applications. Slew rate limited versions also include receiver input filtering to enhance noise immunity in the presence of slow input signals.

The ISL3170E, ISL3171E, ISL3173E, ISL3174E, ISL3176E, ISL3177E are configured for full duplex (separate Rx input and Tx output pins) applications. The half duplex versions multiplex the Rx inputs and Tx outputs to allow transceivers with output disable functions in 8 Ld packages.

Applications

Automated utility meter reading systems

High node count systems

Field bus networks

Security camera networks

Building environmental control/lighting systems

Industrial/process control networks

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