ESP8266 下载模式 GPIO 研究

首先找到ESP8266 的芯片手册
https://www.espressif.com/zh-hans/products/hardware/esp8266ex/overview
ESP8266EX技术规格表
https://www.espressif.com/sites/default/files/documentation/0a-esp8266ex_datasheet_cn.pdf

nodemcu/nodemcu-devkit-v1.0 管脚布局图
https://github.com/nodemcu/nodemcu-devkit-v1.0

管脚布局

管脚号	名称	类型	管脚	功能
1	VDDA	P		Analog Power 2.5V ~ 3.6V
2	LNA	I/O		RF antenna interface Chip output impedance=39+j6 Ω. It is suggested to retain theπ-type matching network to match the antenna.
3	VDD3P3	P		Amplifier Power 2.5V ~ 3.6V
4	VDD3P3	P		Amplifier Power 2.5V ~ 3.6V
5	VDD_RTC	P		NC (1.1V)
6	TOUT	I		ADC pin. It can be used to test the power-supply voltage ofVDD3P3 (Pin3 and Pin4) and the input power voltage of TOUT(Pin 6). However, these two functions cannot be used simultaneously.
7	CHIP_PU	I		Chip Enable High: On, chip works properly Low: Off, small current consumed
8	XPD_DCDC	I/O	GPIO16	Deep-sleep wakeup (need to be connected to EXT_RSTB);GPIO16
9	MTMS	I/O	GPIO14	HSPI_CLK
10	MTDI	I/O	GPIO12	HSPI_MISO
11	VDDPST	P		Digital/IO Power Supply (1.8V ~ 3.6V)
12	MTCK	I/O	GPIO13	HSPI_MOSI; UART0_CTS
13	MTDO	I/O	GPIO15	HSPI_CS; UART0_RTS
14	GPIO2	I/O	GPIO2	UART Tx during flash programming;
15	GPIO0	I/O	GPIO0	SPI_CS2
16	GPIO4	I/O	GPIO4
17	VDDPST	P		Digital/IO Power Supply (1.8V ~ 3.6V)
18	SDIO_DATA_2	I/O	GPIO9	Connect to SD_D2 (Series R: 200Ω); SPIHD; HSPIHD; GPIO9
19	SDIO_DATA_3	I/O	GPIO10	Connect to SD_D3 (Series R: 200Ω); SPIWP; HSPIWP; GPIO10
20	SDIO_CMD	I/O	GPIO11	Connect to SD_CMD (Series R: 200Ω); SPI_CS0; GPIO11
21	SDIO_CLK	I/O	GPIO6	Connect to SD_CLK (Series R: 200Ω); SPI_CLK; GPIO6
22	SDIO_DATA_0	I/O	GPIO7	Connect to SD_D0 (Series R: 200Ω); SPI_MISO; GPIO7
23	SDIO_DATA_1	I/O	GPIO8	Connect to SD_D1 (Series R: 200Ω); SPI_MOSI; GPIO8
24	GPIO5	I/O	GPIO5
25	U0RXD	I/O	GPIO3	UART Rx during flash programming; GPIO3
26	U0TXD	I/O	GPIO1	UART Tx during flash programming; GPIO1; SPI_CS1
27	XTAL_OUT	I/O		Connect to crystal oscillator output, can be used to provide BT clock input
28	XTAL_IN	I/O		Connect to crystal oscillator input
29	VDDD	P		Analog Power 2.5V ~ 3.6V
30	VDDA	P		Analog Power 2.5V ~ 3.6V
31	RES12K	I		Serial connection with a 12 kΩ resistor and connect to the ground
32	EXT_RSTB	I		External reset signal (Low voltage level: active)

启动模式

GPIO2, GPIO0, and GPIO15 are configurable on PCB as the 3-bit strapping register that determines the
booting mode and the SDIO timing mode.

Flash Boot 的意思应该是从Flash启动

串口

串口号	管脚名称	管脚号	IO类型	功能
UART0	U0RXD	25	IO3	U0RXD
UART0	U0TXD	26	IO1	U0TXD
UART0	MTDO	13	IO15	U0RTS
UART0	MTCK	12	IO13	U0CTS
UART1	GPIO2	14	IO2	U1TXD
UART1	SD_D1	23	IO8	U1RXD

UART0 can be used for communication. It supports fluid control. Since UART1 features
only data transmit signal (Tx), it is usually used for printing log

By default, UART0 outputs some printed information when the device is powered on and booting up. The
baud rate of the printed information is relevant to the frequency of the external crystal oscillator. If the
frequency of the crystal oscillator is 40 MHz, then the baud rate for printing is 115200; if the frequency of
the crystal oscillator is 26 MHz, then the baud rate for printing is 74880. If the printed information exerts
any influence on the functionality of the device, it is suggested to block the printing during the power-on
period by changing (U0TXD, U0RXD) to (MTDO, MTCK).

外接SPI Flash

In the QUAD mode flash, 6 IO interfaces are used for flash communication.
In the DUAL mode flash, 4 IO interfaces are used for flash communication.

GPIO

NanoMCU 原理图：

https://www.electrodragon.com/w/images/3/3b/NODEMCU_DEVKIT_V1.0.PDF

MATTERS NEEDING ATTENTION
On every boot/reset/wakeup,
GPIO15 MUST keep LOW, GPIO2 MUST keep HIGH.
GPIO0 HIGH ->RUN MODE, LOW -> FLASH MODE.
When you need to use the sleep mode,GPIO16 and RST should be connected,
and GPIO16 will output LOW to reset the system at the time of wakeup.

nRST 默认为高电平
GPIO0 默认为高电平

原来 DTR 和 RTS 的电平是可以在API控制的
看论坛上好多朋友都很疑惑DTR和RTS线控制电平的问题，我发表个人的见解：
mcuisp下载软件所设置的DTR和RTS是针对RS232C接口的，而战舰开发板上的DTR#和RTS#是CH340芯片输出的。由于232芯片和CH340逻辑反向，因此CH340芯片上的DTR#和RTS#线应该和下载软件上的设置取反。
然后我们看看下载过程：DTR#高电平—-RTS#低电平（BOOT0为1，同时RESET）—-DTR#低电平（释放RESET）—-开始下载—-下载完成后两条线恢复高电平，再次复位同时BOOT0=0，即可正常启动。
http://www.openedv.com/posts/list/0/41396.htm

ESP8285解析

https://arduino-esp8266.readthedocs.io/en/latest/boards.html#generic-esp8266-module
芯片手册：
https://www.espressif.com/sites/default/files/0a-esp8285_datasheet_en_v1.0_20160422.pdf

Generic ESP8285 Module
ESP8285 (datasheet) is a multi-chip package which contains ESP8266 and 1MB flash. All points related to bootstrapping resistors and recommended circuits listed above apply to ESP8285 as well.

Note that since ESP8285 has SPI flash memory internally connected in DOUT mode, pins 9 and 10 may be used as GPIO / I2C / PWM pins.

ESP8255 是芯片内部封装了一个ESP8266 和一个1MB的flash，对应的管脚pin8 之类的已经被占用了。
可以对应 ESP8266 外接一个1MB的SPI FLash的板子正常使用，对等使用。