What is the role of ALE signaling?

ALE is the abbreviation of Adress Lock Enable, single-chip microcomputer P2 is the high octapole address bus, and P0 is the time-sharing multiplexing address, data bus (control the lower octa-bit), the so-called time-sharing multiplexing means that in a time series, different times P0 plays different roles, which requires our ALE to latch the address signal output by PO when it plays the address role.

Address latch signal, which is used to latch the address when reading the external memory.

ALE is the abbreviation of address lock enable, which means the allowed side of address lock.

The ALE of the MCS-51 microcontroller is the address latch signal, and each machine cycle outputs two positive pulses. When accessing the off-chip memory, the falling edge is used to control the external address latch latching the lower 8-bit address output from the P0 port. When no external memory is connected, the output of this pin can be used as a clock signal.

It can also be used to access external memory, such as RAM and ROM.

MCS-51 microcontroller has an external bus, a 16-bit address line, and an 8-bit data line, but the lower 8 bits of the address coincide with the data line, so it is necessary to distinguish the low 8 bits (P0 port, the high 8 bits are P2 ports) address and data when accessing, which requires the use of ALE signals.

When accessing the memory, P2 outputs a high address, and P0 outputs a low address. Use an external latch (usually 74LS373) with ALE pulse to latch the P0 address, at this time the read and write signal starts to work (WR or RD), and the P0 port reads or outputs data. Throughout the process, the data on the address bus of the external memory is always stable, and the lower 8-bit address is stabilized by the ALE and the external latch.

The current 51 generally rarely uses external memory or similar peripherals that use external buses, so most of the current 51 microcontrollers can be set by software to enable the ALE pulse, and the user decides whether to output the ALE pulse, one is to reduce EMI, and the other is to have one more IO port (if ALE is multiplexed).

Parallel port, which is generally used in places where synchronous data is used. Expand RAM or anything.

ALE runs automatically, so you don't have to worry about it in the program.

By the way, what is the difference between the address and data output by the microcontroller to the latch, aren't they all binary numbers?"

Although they are all base data, but the meaning is different, and the location is different, as an address, it acts on the address side of the chip, as data, it acts on the data side, there is a timing problem here, just like the same male teacher, for the son and for the student, the meaning is different, in the face of different people, at different times, the role of this man is different.

This involves the knowledge of counting electricity, you are a freshman, I guess you didn't learn to count electricity, and when you learn, you will understand.

Let me briefly say that if you want to understand it deeply, you have to look at the textbook of digital electricity.

51 single-chip microcomputer is different from other single-chip microcomputer, his data port and the lower 8 bits of the address port are the same port, both are p0 ports, so, how to distinguish p0 is data or address at this time? This is done by introducing a latch.

For example, let's say I write a data "0xaa" to an address with an address of 0xee55"

Here's how the steps go by:

1 ALE controls the latch and allows latch tracking.

Port 2 and P0 have 0xee55 joint output addresses, where P2 outputs 0xee and P0 outputs 0x55

3 The ale level is flipped, and the latch is disabled, that is, at this time, the output of the latch does not change in any way, so the chip address remains unchanged, and it is still "0xee55"

4 p0 port outputs data"0xaa"At this time, the data side of the chip appears"0xaa"After the above steps, the 0xaa is deposited into the address 0xee55.

The above process is carried out automatically by the microcontroller, without the special interference of the program, if executed:

unsigned char xdata *p = unsigned char xdata *)0xee55;

p = 0xaa;

The single-chip microcomputer automatically carries out the above 4-step process, and the ALE, P0, and P2 ports are automatically changed.

It is also translated as ale wine, ale wine, a kind of beer, after grinding the malt, adding brewer's yeast to make it by warm fermentation.

Ale beer is relatively high-temperature fermented beer (above room temperature), with a fast fermentation rate, a short storage period and a high temperature. In the UK, ales are often produced using malt that dissolves very well and is also dark in color, so the color of this beer is also dark.