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Embedded must learn! Detailed explanation of hardware resource interface - based on arm am335x development board (Part 2)

2022-06-28 02:19:00 【Tronlong】

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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 .

LCD Interface

CON15 by LCD Resistive touch screen interface , use 40pin FFC The connector , spacing 0.5mm.

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Design considerations ：

The evaluation board is powered on by default GPE0（ Backlight enable ） Pin , When designing the backplane, please confirm whether it supports power on enabling according to the optional screen LCD Backlight . If it is necessary to control by software LCD Backlight function , It is recommended to use GPIO Pin to control GPE0, And the external default pull-down turns off the backlight enable .
adopt C12/MCASP0_AHCLKR/ECAP2_IN_PWM2_OUT/GPIO3[17] Pin out PWM control LCD Backlight , External pull-down 4K7 Resistance to ground .

KEY

The evaluation board has 5 A button , contain 1 System reset buttons (KEY1,WARM RESET)、1 Power reset buttons (KEY2,POWER ON)、1 Wake up button （KEY3,WAKE UP)、1 Unshielded interrupt keys (KEY4,nMNI)、1 User input keys (KEY5,USER).

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Design considerations ：

（1）RESETn_IN Input for the reset of the core board , A pull-up resistor has been designed inside the core board 10K, It can be suspended by default .

（2）PMIC_POWERON Directly by the PMIC Of PMIC_PB_IN Pin out , Long press 8s above PMIC Will remain reset , Release the key and touch it again ,PMIC Power on the core power again .PMIC_PB_IN stay PMIC The interior has been pulled up 100K Resistance to 5V, It can be suspended by default .

（3）C5/EXT_WAKEUP Direct connection AM335x Of EXT_WAKEUP Pin , Only used for RTC-Only Pattern （ The system defaults to Active Pattern ）. The core board has been designed to pull up 10K Resistance to 1.8V, It can be suspended by default .

（4）B18/nNMI It is an unshielded interrupt function , A pull-up resistor has been designed inside the core board 10K, It can be suspended by default .

A serial port

The evaluation board has 3 A serial port ,CON4 by USB TO UART3,CON6 by RS232 UART0,CON8 by RS485 UART1.

USB TO UART3 A serial port

adopt CH340T The chip will UART3 Turn into Micro USB Interface , Used as a serial port for system debugging .

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RS232 UART0 A serial port

adopt SP3232EEY The serial port level conversion chip will UART0 Convert to RS232 A serial port , Use 9 The needle DB9 Interface .

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RS485 UART1 A serial port

By isolating the transceiver ISO3082DW, take UART1 Convert to RS485 A serial port , Interface to use 3pin 3.81mm Green terminal mode .

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Micro SD Interface

CON5 by Micro SD Card interface , adopt MMC0 Bus out , use 4bit Data line mode .

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Design considerations ：

Need to TF Of the housing SHIELD[1:4] Receive digital .

RTC

CON3 by RTC seat , Adaptive button battery ML2032（3V Rechargeable ）.RTC Circuit usage DS1340Z-33+ The chip implements external RTC function , adopt I2C0 The bus is connected to CPU.

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Design considerations ：

If you need to use a non rechargeable button battery CR2032, Please put D2 Diodes and R83 The resistor is empty .

USB Interface

CON1 and CON11 It's two-way USB 2.0 HOST Interface , Double layer Type-A Type connector ,CON10 by USB 2.0 DRD, use Micro USB The connector .

USB 2.0 HOST Interface

adopt USB 2.0 HUB The chip will USB0 Bus (USB 2.0) Expand into 4 road USB 2.0 HOST Interface .

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USB 2.0 DRD Interface

USB 2.0 DRD Directly by the USB1 Bus (USB 2.0) extraction , Support software switching to HOST or DEVICE Pattern .

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Design considerations ：

（1）F15/USB1_DRVVBUS Pins can be used as USB1 Of DRVVBUS or GPIO function , The evaluation board is used as USB1 Of DRVVBUS function .

Ethernet Interface

CON18 by RGMII1 ETH Gigabit Internet port ,CON19 by RGMII2 ETH Gigabit Internet port .RJ45 The connector has built-in isolation transformer .

AM335x Internal integration 2 individual GMAC controller , Support 2 road RGMII Gigabit Internet port . because RGMII2 And MII1_PRUSS1 The bus has a pin reuse relationship , Therefore, the following network circuit configurations can be supported in the backplane design ：

2 road RGMII Gigabit Internet port .
2 road RGMII Gigabit Internet port 、1 road PRU 100m network port （ Limited to AM3359）.
1 road RGMII Gigabit Internet port 、2 road PRU 100m network port （ Limited to AM3359）.

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Design considerations ：

RGMII The bus and transceiver are connected in series 22R resistance .
Analog power supply and digital power supply are isolated by magnetic beads .1.2V The power supply scheme shall meet 500mA Power requirements , It is recommended to refer to the evaluation board DCDC programme , If you need to use LDO programme , Pay attention to thermal design , avoid LDO It's too hot .
XI、XO Pin access 25MHz Passive crystal oscillator . For the convenience of crystal oscillator starting ,XI、XO Parallel connection can be added between 1MΩ resistance . If you want to use 25MHz Active crystal oscillator , Can be obtained from XI Pin access ,XO Pin suspension processing .
KSZ9031RNXIA The chip requires that after the power supply is stable , keep 10ms Then pull up the reset signal . It is recommended to evaluate the reset circuit scheme of the backplane .

HDMI OUT Interface

J1 by HDMI OUT Video output interface .HDMI adopt I2C1 To configure , among CPI of HDMI Transmitter Of I2C The address is 0x3B,TPI of HDMI Transmitter Of I2C The address is 0x62.

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Design considerations ：

E17/I2C1_SCL/GPIO1[9]、E18/I2C1_SDA/GPIO[8] The pin has been pulled up on the evaluation backplane 2.2K Resistance to 3.3V Power Supply .
Do not HDMI Output of the pedestal VDD_5V_HDMICONN The power supply is used to supply power to other loads .
HDMI Seat HPLG The signal needs to be pulled down 10K Resistance to ground , When an external device is connected , Will pull this signal high .

CAN Interface

CON9 by CAN0 Interface , use 3pin 3.81mm Green terminal mode .

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FRAM

U9 by FRAM Ferroelectric chip , The size is 512Byte, Can be used to store user configuration data , Connect to I2C0 Bus , Two pages I2C The equipment addresses are respectively 0x50 and 0x51.

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Design considerations ：

I2C0 It has been designed inside the core board 4.7K Pull up resistance , The pull-up resistance may not be designed in the design of the base plate .

ADC Interface

J2 by 1x 8-ch 12-Bit ADC Interface ,200K Samples Per Second,2x 5pin How to arrange needles , spacing 2.54mm, The voltage input range is generally 0~1.8V.

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Design considerations ：

ADC The input voltage range is 0~1.8V, During design, it should be noted that the input signal should not exceed the above requirements , Otherwise, the core board may be damaged .