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ID A11C: Hardware Design Fundamentals for MCU-based Embedded Systems Renesas Electronics America Inc. Mitch Ferguson Manager, Application Engineering 12 October 2010 14 October 2010 © 2010 Renesas Electronics America Inc. All rights reserved. Version 1.0 Mr. Mitch Ferguson Applications Engineer Manager Specializes support design teams develop low-noise systems using MCUs. Over 15 years of system-level design experience Over 7 years of experience as an application engineer. As a hardware engineer and engineering manager, he has been involved in design in power distribution controls, automotive and fire alarm systems with focus on EMI/EMS issues. Bachelor of science in electrical engineering from Cleveland State University 2 © 2010 Renesas Electronics America Inc. All rights reserved. Renesas Technology and Solution Portfolio Microcontrollers & Microprocessors #1 Market share worldwide * ASIC, ASSP & Memory Advanced and proven technologies Solutions for Innovation Analog and Power Devices #1 Market share in low-voltage MOSFET** * MCU: 31% revenue basis from Gartner "Semiconductor Applications Worldwide Annual Market Share: Database" 25 March 2010 ** Power MOSFET: 17.1% on unit basis from Marketing Eye 2009 (17.1% on unit basis). 3 © 2010 Renesas Electronics America Inc. All rights reserved. Renesas Technology and Solution Portfolio Microcontrollers & Microprocessors #1 Market share worldwide * Solutions for Innovation ASIC, ASSP & Memory Advanced and proven technologies Analog and Power Devices #1 Market share in low-voltage MOSFET** * MCU: 31% revenue basis from Gartner "Semiconductor Applications Worldwide Annual Market Share: Database" 25 March 2010 ** Power MOSFET: 17.1% on unit basis from Marketing Eye 2009 (17.1% on unit basis). 4 © 2010 Renesas Electronics America Inc. All rights reserved. Microcontroller and Microprocessor Line-up Superscalar, MMU, Multimedia High Performance CPU, Low Power High Performance CPU, FPU, DSC Up to 1200 DMIPS, 45, 65 & 90nm process Video and audio processing on Linux Server, Industrial & Automotive Up to 500 DMIPS, 150 & 90nm process 600uA/MHz, 1.5 uA standby Medical, Automotive & Industrial Up to 165 DMIPS, 90nm process 500uA/MHz, 2.5 uA standby Ethernet, CAN, USB, Motor Control, TFT Display Legacy Cores Next-generation migration to RX General Purpose Up to 10 DMIPS, 130nm process 350 uA/MHz, 1uA standby Capacitive touch 5 © 2010 Renesas Electronics America Inc. All rights reserved. Ultra Low Power Embedded Security Up to 25 DMIPS, 150nm process Up to 25 DMIPS, 180, 90nm process 190 uA/MHz, 0.3uA standby 1mA/MHz, 100uA standby Application-specific integration Crypto engine, Hardware security Microcontroller and Microprocessor Line-up Superscalar, MMU, Multimedia High Performance CPU, Low Power High Performance CPU, FPU, DSC Up to 1200 DMIPS, 45, 65 & 90nm process Video and audio processing on Linux Server, Industrial & Automotive Up to 500 DMIPS, 150 & 90nm process 600uA/MHz, 1.5 uA standby Medical, Automotive & Industrial Up to 165 DMIPS, 90nm process 500uA/MHz, 2.5 uA standby Ethernet, CAN, USB, Motor Control, TFT Display Legacy Cores Next-generation migration to RX General Purpose Up to 10 DMIPS, 130nm process 350 uA/MHz, 1uA standby Capacitive touch 6 © 2010 Renesas Electronics America Inc. All rights reserved. Ultra Low Power Embedded Security Up to 25 DMIPS, 150nm process Up to 25 DMIPS, 180, 90nm process 190 uA/MHz, 0.3uA standby 1mA/MHz, 100uA standby Application-specific integration Crypto engine, Hardware security Innovation I-Cache 32KB D-Cache 32KB L2 Cache 256KB MMU UBC INTC DMAC x6 H-UDI CPG 500MHz 900 MIPS FPU MAC LCDC Others WDT TMU x3 (ROM/SRAM) VOU VPU5F H.264 D1@60fps 720p@30 2DG 32/16bit SCIF x6 CEU x2 (Camera I/F) GPIO 10/100 Ethernet MAC w/DMA CPU I2C x2 SDIO x2 MEMORY BEU x2 (Blend) ANALOG © 2010 Renesas Electronics America Inc. All rights reserved. MMC NAND KeyScan JPEG IrDA SPU ATAPI 24bit DSP TIMER Integration 7 DDR2 VEU x2 (Scaling) USB-HS Host or Device w/PHY x2 BSC Multi media I/O Integration has made hardware easier but not something that can be ignored 8 © 2010 Renesas Electronics America Inc. All rights reserved. Agenda Selecting clock circuit Power-On Reset (POR) and Low Voltage Detect (LVD) Watch Dog Timer (WDT) requirements Input Circuits Output Circuits 9 © 2010 Renesas Electronics America Inc. All rights reserved. How much time do you spend designing hardware 10 1. Firmware Only 2. Both Hardware and Firmware 3. Hardware Engineer 4. Architecture Level only © 2010 Renesas Electronics America Inc. All rights reserved. Clock Circuit Selection Clocking circuit criteria Startup time Accuracy Reliability Cost Clock alternatives 11 Crystal Ceramic Resonator On-Chip Oscillator Compensated External Oscillator (TXO) © 2010 Renesas Electronics America Inc. All rights reserved. Clock Comparison – Arranged Best to Worst Best Cost Reliability External (±25 ppm or better) On-Chip On-Chip On-Chip (<10 cycles) Crystal (±50-200 ppm) Resonator ($0.16) w/caps Resonator Resonator (100 uS) Crystal ($0.20) Crystal/ External Crystal (1-5 mSec) Resonator (>0.5% ) Worst Startup Time Accuracy On-Chip (>2%) External ($2.91) External (10 mSec) 0.5% = 5000 ppm Rev. 1.00 12 © 2010 Renesas Electronics America Inc. All rights reserved. Clock Requirements – A few points Standard OCO Resonator Special Resonator Crystal TXO CAN Clock -3.6 hr lost/month Clock 30 min lost/yr USBFS USBHS Uart 5% 1% Ethernet 0.5% 0.1% 0.05% 0.01% 0.005% 5000ppm 500 ppm Accuracy of Clock 13 © 2010 Renesas Electronics America Inc. All rights reserved. Power RF 50 ppm Power On Reset (POR) Do we need a POR circuit ? YES – you always need some POR POR Options Simple RC Internal POR External POR 14 © 2010 Renesas Electronics America Inc. All rights reserved. Simple RC Power On Reset Advantages Vcc Inexpensive Simple Disadvantages Very dependent on Vcc rise time Not so simple Let’s look at an example Design an RC circuit for M16C/62P 15 © 2010 Renesas Electronics America Inc. All rights reserved. MCU Reset RC Power On Reset Example Requirements (M16C/62P example) Reset <0.2 * Vcc for 2 mSec after min operating voltage Difficult if Vcc rises slowly Assume Vcc “snaps” to V operating Vreset = Vcc (1-e-TC) Min Op Voltage Vcc 1 TC = 0.63 Vcc 0V 0.2 TC = 0.2 Vcc 0.2 Vcc Reset 0V > 2mSec 16 © 2010 Renesas Electronics America Inc. All rights reserved. This means RC design must have 10 mSec TC External Power On Reset Options Purchase a POR/Voltage Monitor Chip Design your own Purchased device Advantage – Simple – Reliable Disadvantage – Cost – Must match to the MCU 17 © 2010 Renesas Electronics America Inc. All rights reserved. External Power On Reset (Cont)VCC Design your own R1 Advantage 10K – Cost ? Res et Disadvantage Can be tricky to design Multiple components R2 47K 2.7V R3 100K C1 2.2 uF Zener set for MCU Vmin Appendix has a full calculation R3 >> R2 Reset Line slope dV/dT is approximately [(Vz-0.6)/R2)]/C1 18 © 2010 Renesas Electronics America Inc. All rights reserved. On-Chip Power On Reset Advantage Cost Already “tuned” to MCU Disadvantages MCU must have a POR May have rise time limitations on Vcc 19 © 2010 Renesas Electronics America Inc. All rights reserved. On-Chip Power On Reset - Example R8C/23 2.7 mA will charge 100 uF of capacitance to 2.7V in less than 100 mSec 20 © 2010 Renesas Electronics America Inc. All rights reserved. Low Voltage Detector (LVD) - (Brown-out Detect) Do I need an LVD circuit? Probably Purpose of LVD Prevent operation of MCU with Voltage < Vcc min Anticipate loss of voltage – Save data – Place system in “safe” state LVD only monitor MCU Vcc Consider all system power sources 21 © 2010 Renesas Electronics America Inc. All rights reserved. An example of using Voltage Detect Slow Clock, Save Data to EEPROM Vcc 3.3-3.9 Vdet2 Vdet1 2.7-3.0 Power down mode entered Restore Data, Run Full Speed Clock 2.6 POR Exit power down mode Operating Range 3.0 – 5.5 20 MHz 2.7 – 3.0 10 MHz 22 © 2010 Renesas Electronics America Inc. All rights reserved. Ride Through Backup is not always Battery Example Ride through 30 seconds Do Not use Battery Allow Voltage drop 3.1 to 2.8 Icc at 2 MHz = 1.5 mA To system 3.6V SuperCap 0.1 uF Vcc R8C/27 I = C dV/dT C = (I * dT)/dV C = 0.15 Farad * Above 0.22F @ 3.3V not common 23 © 2010 Renesas Electronics America Inc. All rights reserved. Watchdog Timer – Internal or External The internal WDT Recovers from software errors Don’t expect recovery from noise External WDT Sometimes required by safety standard Better chance recovering from noise Contained in many Voltage Monitors 24 © 2010 Renesas Electronics America Inc. All rights reserved. Input Circuits – Connecting Switches Physical connection, pull-up or pull-down Internal Pull-ups ? V+ V+ Vcc Vcc R MCU Input Interrupt or no Interrupt 25 © 2010 Renesas Electronics America Inc. All rights reserved. Input MCU R Pull–ups – How large can they be? Assume GPIO requires 0.8 Vcc for Vih V+ Use Vcc 3.0V for battery Pin leakage current 1.0 uA max Vcc R MCU Input Max resistance for pullup = 600 K (.6V/.1uA) Typically use between 10K and 68K 26 © 2010 Renesas Electronics America Inc. All rights reserved. Pull–ups when power is critical V+ Vcc Output S1 causes power loss when closed 3V/600K = 5 uA R Use port pin to drive pull-up Drive pin low once S1 active Poll status of S1 when active 27 © 2010 Renesas Electronics America Inc. All rights reserved. MCU Input S1 Level Translation Problem - Interfacing a 3V micro design to 5V LCD Writing to LCD R8C Voh is (Vcc – 0.5V) @ 5 mA No Problem 28 © 2010 Renesas Electronics America Inc. All rights reserved. Level Translation - Reading Unfortunately, R8C inputs are not 5V tolerant +3.3V +5V R2 MCU R1 = 30K R2 = 20K 29 © 2010 Renesas Electronics America Inc. All rights reserved. R1 LCD What about the other way It is a little different when MCU voltage is higher MCU requires 0.8 * Vcc (this is standard CMOS) +5V GPIO +3V R1 10K R2 MCU 30 © 2010 Renesas Electronics America Inc. All rights reserved. 4.7K Sensor Switch A Power Output Designing a simple power drive Get Load requirement Divide by port output current This gives minimum hFE or Beta R2 = (Vout - 0.6)/(rated output current of port pin) D1 rated at load current +12V D1 +3V Load R2 680 31 © 2010 Renesas Electronics America Inc. All rights reserved. MCU Unused Inputs Options Check HW manual Pull up or down – Preferable to pull low Set to output – Set output and low – Vulnerable until set – Draws power until set 32 © 2010 Renesas Electronics America Inc. All rights reserved. Questions? 33 © 2010 Renesas Electronics America Inc. All rights reserved. Summary Selecting clock circuit POR/LVD WDT requirements Input Circuits Output Circuits 34 © 2010 Renesas Electronics America Inc. All rights reserved. Innovation I-Cache 32KB D-Cache 32KB L2 Cache 256KB MMU UBC INTC DMAC x6 H-UDI CPG 500MHz 900 MIPS FPU MAC LCDC Others WDT TMU x3 (ROM/SRAM) VOU VPU5F H.264 D1@60fps 720p@30 2DG 32/16bit SCIF x6 CEU x2 (Camera I/F) GPIO 10/100 Ethernet MAC w/DMA CPU I2C x2 SDIO x2 MEMORY BEU x2 (Blend) ANALOG © 2010 Renesas Electronics America Inc. All rights reserved. MMC NAND KeyScan JPEG IrDA SPU ATAPI 24bit DSP TIMER Integration 35 DDR2 VEU x2 (Scaling) USB-HS Host or Device w/PHY x2 BSC Multi media I/O Appendix - 36 © 2010 Renesas Electronics America Inc. All rights reserved. To Interrupt or Not Probably Not Switches – except for low power wake-up A/D SPI Probably UART Receive/Transmit Timers Pulse counting or edge detection 37 © 2010 Renesas Electronics America Inc. All rights reserved. Polled Switch Routine Use Timer Tick for scheduling Setup below for 1 mSec tick Samples switch every 5 mSec if ((tick_timer - last_sample_time)>4)){ if (SW1 ) SW1_count++; else SW1_count = 0; if (SW1_count > 5){ SW1_state = ACTIVE; . . . last_switch_sample = tick_timer; 38 © 2010 Renesas Electronics America Inc. All rights reserved. External Power On Reset (Cont) VCC Assume Q beta = 75 Vcc = 5V, Vmin = 2.7V R1 Set C1 to 0.22 uF Charge time 10 mSec for 2.7V charge I= C dv/dt = 0.22 uF * 0.5V/2mS = 50 uA R1 sets zener current . Typical 0.5 ma current would need 10K R2 = (2.7V – 0.6)/50 uA = 42K R3 just a discharge path 100K R2 Res et R3 C1 Zener set for MCU Vmin R3 >> R2 Reset Line slope dV/dT is approximately [(Vz-0.6)/R2)]/C1 39 © 2010 Renesas Electronics America Inc. All rights reserved. Renesas Electronics America Inc.