1
Small external bus such as single chip microcomputer
Small MCUs such as single-chip microcomputers generally have an external bus, which can be used to connect a true color LCD (asynchronous bus interface TFT display). Most of the phones use a screen that synchronizes (first give an address, then continuously brush the data) interface.
2
ARM processor application scenario
ARM7: industrial control, mobile phone;
ARM9: image display;
Cortex-A: High-performance applications: mobile phones, cottages;
Cortex-M: low-end applications;
Cortex-R: Mid-range applications are relatively rare.
3
ARM processor exception
In general, some of the previous interrupts (such as the first 15) are designed by ARM itself and are fixed. The middle part of the latter part is defined by different chip manufacturers.
4
Processor's System Timer
The System Timer, Systick, can be used as a general-purpose timer when there is no OS. When the OS is required, it can be used as the system clock of the OS.
5
The prohibition and enable of the same interrupt are respectively
Different register controls
At present, there are many phenomena in the processing, and the prohibition and enable of the same interrupt are controlled by different registers. When the interrupt is disabled, write 1 to the corresponding bit in the interrupt mask register. When the interrupt is enabled, write 1 to the corresponding bit in the interrupt enable register.
The benefits of this separate control are:
A. Do not read out the value of the interrupt control register first, then perform the operation and then write it back.
B. Write 1 directly, it will not affect the interrupt controlled by other bits.
6
OD gate output
Can be used when the processor level does not match the peripheral level.
7
How to set the state of IO to reduce power consumption
If an input pin is left floating, there is leakage current, which will consume power. Judgment method: When you touch it by hand, the current will change.
A. Set the unused pins to the output mode of 0 or 1.
B. If configured as an input pin, the internal pull-up should be turned on.
8
ADC and DAC
The ADC and DAC should be turned off while the system is sleeping, otherwise power will be consumed.
9
Use of watchdog
A. Don't feed the dog in the interruption.
B. The more regular the dog is, the better.
10
I2C bus
Both SDA and SCL are bidirectional, open-drain driven, and must be pulled with a pull-up resistor.
I2C protocol communication process:
A. Send start signal (who sends the start signal, who is the host)
B. Send the slave address
C. Transferring data
D. Send stop signal
The I2C bus emulated by software has the following disadvantages:
A. Cannot perform bus arbitration
B. It is difficult to implement the slave device because the clock signal is always detected.
11
Logic 0 page
The logic 0 pages of many MCUs can be arbitrarily mapped so that multiple systems can be programmed in flash. The configuration can be implemented by configuring the byte configuration system to boot from a different address.
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