51 Single Chip Microcomputer pin ale/prog/psen/EA/VPP
Reprinted from:Http://www.how138.com/news.asp? Id = 576
Four control pins of 51 single-chip microcomputer, one of which is the reset pin (RST/VPD)
RST is the reset pin. When the RST input end maintains two or more machine cycles, It is reset.
Ale/prog is the allowable output end of the address lock memory. It is used to lock 8-bit address signals when reading and writing external memory.
When the microcontroller works normally, Ale outputs a fixed pulse signal at 1/6 of the clock oscillation frequency.
The second feature, prog, is 8751 solid for a 4 k eprom in the chip.ProgramAs the input of the programming pulse.
Psen is the read-selected communication number of the off-chip program memory, which is effective at a low level. When the CPU obtains instructions from the external program memory, the psen signal will automatically generate a negative pulse, the selected communication number as the external program memory.
EA/VPP: When the EA is high, the CPU executes in-chip program memory commands. When the Pc value exceeds 0ffffh, the off-chip program memory commands are automatically executed;
When the EA is low, the CPU only executes off-chip program memory commands.
The following content is reproduced in Baidu Encyclopedia: Ale/prog address lock control signal When the system is extended, ale is used to control the low 8-bit output address of P0 port to send latches to lock up, so as to isolate the low address and data. (In the subsequent extended courses, we will see the 8051 extended EEPROM circuit. in the figure below, the ale is connected to the G of the 74LS373 latch. When the CPU accesses the outside, the low address used to lock the address, that is, the P0 port output. Ale may be high or low. When ale is high, the address lock signal is allowed. When the access to the external memory, the ale signal is changed to a negative hop (from positive to negative) send the eight-bit lower address signal of the P0 port to the latch. When ale is low, the content on the P0 port is the same as that on the latch output. We will introduce the content of latches later. When the external memory is not accessed, the ale outputs at a frequency of 1/6 oscillation cycle (that is, 6-frequency division), when the access to the external memory is output at a frequency of 1/12 oscillation cycle (12-Frequency Division ). From this we can see that when the system is not extended, Ale will output at a fixed frequency of 1/6 oscillation cycle, so it can be used as an external clock or an external scheduled pulse. Porg is the input of the programming pulse. Lesson 5
The internal structure and composition of the single chip microcomputer, we know that there is a 4 kb or 8 KB program memory (ROM) in the 8051 single chip microcomputer ), rom is used to store the program that the user needs to execute. So how do we store the compiled program into this Rom? In fact, it can be written through the programming pulse input. The input port of this pulse is prog.
Psen external program memory read selected communication number : When reading external Rom, psen is effective at a low level to implement read operations on external Rom units. 1. psen does not act when the internal ROM is read; 2. When the external Rom is read, psen will act twice in each machine cycle; 3. When the external Ram is read, two psen pulses are skipped and will not be output. 4. When an external Rom is used, it is connected to the OE foot of the Rom. See figure 2-(8051 eXtended 2 kb EEPROM circuit, in the figure psen is connected to the OE foot of the extended ROM) EA/VPP access and sequential memory control signal 1. Access to high-voltage normally: CPU read internal program memory (ROM) extended external ROM: When the read internal program memory exceeds 0 fffh (8051) 1 fffh (8052), the external Rom is automatically read. 2. Low Power Usage: the CPU reads external program memory (ROM ). In the previous study, we already know that there is no rom In the 8031 microcontroller, so when the 8031 microcontroller is applied, this foot is a direct low level. 3. 8751 when the internal EPROM is burned, use this pin to input a burning voltage of 21 v.
