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MS82C55A 데이터시트(PDF) 3 Page - Intersil Corporation |
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MS82C55A 데이터시트(HTML) 3 Page - Intersil Corporation |
3 / 24 page 3 FN6140.1 June 28, 2005 Functional Diagram Functional Description Data Bus Buffer This three-state bidirectional 8-bit buffer is used to interface the 82C55A to the system data bus. Data is transmitted or received by the buffer upon execution of input or output instructions by the CPU. Control words and status information are also transferred through the data bus buffer. Read/Write and Control Logic The function of this block is to manage all of the internal and external transfers of both Data and Control or Status words. It accepts inputs from the CPU Address and Control busses and in turn, issues commands to both of the Control Groups. (CS) Chip Select. A “low” on this input pin enables the communication between the 82C55A and the CPU. (RD) Read. A “low” on this input pin enables 82C55A to send the data or status information to the CPU on the data bus. In essence, it allows the CPU to “read from” the 82C55A. (WR) Write. A “low” on this input pin enables the CPU to write data or control words into the 82C55A. (A0 and A1) Port Select 0 and Port Select 1. These input signals, in conjunction with the RD and WR inputs, control the selection of one of the three ports or the control word register. They are normally connected to the least significant bits of the address bus (A0 and A1). (RESET) Reset. A “high” on this input initializes the control register to 9Bh and all ports (A, B, C) are set to the input mode. GROUP A PORT A (8) GROUP A PORT C UPPER (4) GROUP B PORT C LOWER (4) GROUP B PORT B (8) GROUP B CONTROL GROUP A CONTROL DATA BUS BUFFER READ WRITE CONTROL LOGIC RD WR A1 A0 RESET CS D7-D0 POWER SUPPLIES +5V GND BIDIRECTIONAL DATA BUS I/O PA7-PA0 I/O PC7-PC4 I/O PC3-PC0 I/O PB7-PB0 8-BIT INTERNAL DATA BUS FIGURE 1. FUNCTIONAL DIAGRAM 82C55A BASIC OPERATION A1 A0 RD WR CS INPUT OPERATION (READ) 00010 Port A → Data Bus 01010 Port B → Data Bus 10010 Port C → Data Bus 11010 Control Word → Data Bus OUTPUT OPERATION (WRITE) 00100 Data Bus → Port A 01100 Data Bus → Port B 10100 Data Bus → Port C 11100 Data Bus → Control DISABLE FUNCTION XXXX 1 Data Bus → Three-State X X 110 Data Bus → Three-State MS82C55A, MQ82C55A |
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