51 illustrating how to use the microcontroller bus address circuit design

Single-chip system with bus expansion interface, including external 32kram extensions, LCDL602 interface, input and output ports. Single-chip microcomputer with address extension is shown below. Using 74HC573 latch low 8-bit address; 74138 implements 8 address extensions, 74138 A, B, C connected A8 ~ A9, E1 connected AL5, E2, E3 grounding is often effective, get OF8FFH to OFFFH8 address or 8000H to 8700h ( Unlocked by 0). The 32K interface is shown below. The DO ~ D7 connection data bus P0 port, the address line AO ​​~ AL4 is connected to the single-chip address bus low, the single-chip address line AL5 pieces are selected, the low level is effective, so that the address is assigned from OOOH to 7FFFH, and the 74138 decoded address is not conflict. The LCD1602 interface circuit is shown below. RS, RW separates AL2, AL3, enabling the signal addressing as Y7, so that the four drive addresses of the LCD (data read / write and command read / write) are Ocfffh to OFFFH (no bites 1) or 8700h to OB70OH (no position 0). Sometimes the single-chip pin is not enough, but also to expand, the input port extension circuit is shown in the figure above, using the high-resistance function of 74HC573 (74LS373), the output Qo ~ Q7 picks up P0 port, in the bus address read operation It can read the data of the input Inport to the accumulator of the microcontroller, the address is OF8FFH or 8000H. The output port extension circuit is shown in the following figure, using the 74LS273 data latch function to meet the bus address write operation. You can write the data in a single-chip tube into 273 latch output, and the address is OF8FFH or 8000H. Since the control bus used is different, the shared address can be entered. Read more

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