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2025-01-27 07:59本頁(yè)面
【正文】 truction set of the 8051, they are RISC instruction set, and only a few dozen instructions, most instructions are single instruction cycle instruction, so in the same crystal frequency, faster than the 8051. Another PIC 8bit microcontroller in previous years, is the world39。 3, external RAM read, the two PSEN pulse is skipped will not be output。s role is to be used to store user needs implementation of the program, then we are into how to write good programs into this ROM in it? Is actually programmed into the pulse input can be written, this pulse input port is PROG. PSEN external program memory read strobe: In reading an external ROM, PSEN low effective, in order to achieve an external ROM module read. 1, the internal ROM reading, PSEN is not action。 Therefore, if the P0 port as long as the input, in the high impedance state, only an external pullup resistor to be effective. ALE / PROG address latch control signal: in a system is extended, ALE is used to control the P0 port output low 8bit address latch latch get together in order to achieve low address and data segregation. (In the back on the expansion of the curriculum, we will see the 8051 expansion of EEPROM circuit, the ALE and the 74LS373 in Figure Glatches connected to the external CPU to access when the time to lock the address low address, the P0 port output. ALE may be high may also be low, when the ALE is high, allowing address latch signal when accessing external memory, ALE signals a negative transition (from positive to negative) P0 port on the lower eight address signals into the latch. when ALE is low, when, P0 port on the content and the output latch line. on the latch, and we will be introduced later. In the absence of access to external memory during the period, ALE 1 / 6 oscillator frequency output cycle (ie, frequency of 6 points), when access to external memory to 1 / 12 oscillator cycle, the output (12 min frequency). From here we can see that when the system does not extend when the ALE will be 1 / 6 cycle, fixed freq
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