Embedded must learn, detailed explanation of hardware resource interface -- Based on arm am335x development board (Part 1)

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This document mainly introduces embedded elementary learners , Using the core board / During the development of the board , Some hardware interface resources and design considerations, etc . This article is based on Dragon technology TL335x-EVM-S Development board , It is based on TI Sitara series AM3352/AM3354/AM3359 ARM Cortex-A8 Evaluation board for high performance and low power processor design .

Evaluation board interface resources are rich , Lead out dual Gigabit network port 、LCD、HDMI、GPMC、CAN Such as the interface , It is convenient for users to quickly carry out product scheme evaluation and technology pre research , Application in communication management 、 Data collection 、 human-computer interaction 、 Motion control 、 Typical fields such as intelligent power .

AM335x Of IO The level standard is generally 3.3V, The pull-up power supply generally does not exceed 3.3V, When the external signal level is equal to IO In case of level mismatch , Level conversion chip or signal isolation chip shall be added in the middle . Keys or interfaces need to be considered ESD Design ,ESD When selecting devices, pay attention to whether the junction capacitance is too large , Otherwise, signal communication may be affected .

SOM-TL335x-S Core board

SOM-TL335x-S On the core board CPU、ROM、RAM、 Crystal oscillator 、 Power management chip 、LED And hardware resources , And led out through the connection of stamp holes IO. Core board hardware resources 、 Pin description 、 Electrical characteristics 、 Mechanical Dimensions 、 Details such as precautions for bottom plate design , Please refer to 《SOM-TL335x-S Core board hardware instructions 》.

chart 3 Hardware block diagram of the core board

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The core board adopts 4x 40pin Connection mode of stamp hole , common 160pin, Pin spacing is 1.0mm.

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The power interface

CON2 by 12V2A DC input DC-417 The power interface , Adaptable outer diameter 4.4mm、 The inner diameter 1.65mm The power plug . The power input has the function of over-current and over-voltage protection .SW1 Swing the switch for the power supply .

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Design considerations ：

1. VDD_12V_MAIN adopt TPS54527DDA（DC-DC Step down chip ） Output VDD_5V_MAIN For core board , Through another way TPS54527DDA Chip output VDD_3V3_MAIN It is used for evaluating baseboard peripherals . To make VDD_3V3_MAIN Meet the power on of the system 、 Power down sequence requirements , Core board output power supply is required VDD_3V3_VAUX2 To control VDD_3V3_MAIN The power supply of the is enabled , Make the base plate VDD_3V3_MAIN The power supply is later than the core board power supply .
2. VDD_5V_MAIN No large energy storage capacitor for total power input is reserved inside the core board , When designing the bottom plate, please place a large energy storage capacitor near the stamp hole .

LED

Evaluate the floor LED0 For power indicator light , The system turns on by default . Evaluate the floor LED1、LED2 and LED3 Programmable indicator for the user , adopt GPIO control , The default high level is on .

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JTAG Interface

CON7 by TI Rev B JTAG Simulation debugging interface , use 14pin Simple horn socket connector , spacing 2.54mm, To fit Tronlong Of TL-XDS100V2、TL-XDS200 and TL-XDS560V2 Emulator .

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Design considerations ：

1. JTAG The signal level of the interface pin is 3.3V.
2. When designing the bottom plate , if JTAG The bus only leads out the test point , When connecting the simulator by flying wire , It is necessary to set the TDIS The pin is connected to the digital ground of the backplane , Otherwise the emulator will not recognize the device .
3. because JTAG Interface does not EMU0/EMU1 The pins are led out to the backplane ,EMU0/EMU1 The pins have been controlled on the core board LED1/LED2, Therefore, this design does not support EMU0/EMU1 A functional test .

BOOT SET Activate the selector dial switch

SW2 by 5bit Start mode selection dial switch . There are two common startup modes , Activate the... Of the selector dial switch ON by 1, On the contrary 0.

1. Micro SD Card boot mode ：00010(1~5)
2. eMMC Boot mode ：11000(1~5)
3. NAND FLASH Boot mode ：10110(1~5)
4. SPI FLASH Boot mode ：10010(1~5)

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Design considerations ：

1. SYSBOOT[4:0] and SYSBOOT9 The pins pass through the evaluation backplane BOOT SET Select the starting mode by starting the dial switch or pull-down resistor .
2. SYSBOOT[15:0] Pin please use the output of the core board VDD_3V3_VAUX2.VDD_3V3_VAUX2 Is dedicated to BOOT SET Configured power supply , Do not use it for power supply of other loads .
3. because SYSBOOT Pin and LCDC The bus has a reuse relationship , If you use LCDC Bus external equipment or other multiplexing functions , Please make sure AM335x During power on initialization SYSBOOT Pin level is not affected by external equipment , Otherwise, it will lead to AM335x Unable to start properly . You can use Buffer(SN74LV244A) Realization AM335x During power on initialization , Isolate external equipment pairs SYSBOOT Influence .