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IS82C55A Datasheet(PDF) 5 Page - Intersil Corporation |
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IS82C55A Datasheet(HTML) 5 Page - Intersil Corporation |
5 / 26 page 5 The modes for Port A and Port B can be separately defined, while Port C is divided into two portions as required by the Port A and Port B definitions. All of the output registers, including the status flip-flops, will be reset whenever the mode is changed. Modes may be combined so that their functional definition can be “tailored” to almost any I/O structure. For instance: Group B can be programmed in Mode 0 to monitor simple switch closings or display compu- tational results, Group A could be programmed in Mode 1 to monitor a keyboard or tape reader on an interrupt-driven basis. The mode definitions and possible mode combinations may seem confusing at first, but after a cursory review of the complete device operation a simple, logical I/O approach will surface. The design of the 82C55A has taken into account things such as efficient PC board layout, control signal defi- nition vs. PC layout and complete functional flexibility to sup- port almost any peripheral device with no external logic. Such design represents the maximum use of the available pins. Single Bit Set/Reset Feature (Figure 5) Any of the eight bits of Port C can be Set or Reset using a single Output instruction. This feature reduces software requirements in control-based applications. When Port C is being used as status/control for Port A or B, these bits can be set or reset by using the Bit Set/Reset operation just as if they were output ports. Interrupt Control Functions When the 82C55A is programmed to operate in mode 1 or mode 2, control signals are provided that can be used as interrupt request inputs to the CPU. The interrupt request signals, generated from port C, can be inhibited or enabled by setting or resetting the associated INTE flip-flop, using the bit set/reset function of port C. This function allows the programmer to enable or disable a CPU interrupt by a specific I/O device without affecting any other device in the interrupt structure. INTE Flip-Flop Definition (BIT-SET)-INTE is SET - Interrupt Enable (BIT-RESET)-INTE is Reset - Interrupt Disable NOTE: All Mask flip-flops are automatically reset during mode se- lection and device Reset. Operating Modes Mode 0 (Basic Input/Output). This functional configuration provides simple input and output operations for each of the three ports. No handshaking is required, data is simply writ- ten to or read from a specific port. Mode 0 Basic Functional Definitions: • Two 8-bit ports and two 4-bit ports • Any Port can be input or output • Outputs are latched • Input are not latched • 16 different Input/Output configurations possible FIGURE 5. BIT SET/RESET FORMAT D7 D6 D5 D4 D3 D2 D1 D0 BIT SET/RESET 1 = SET 0 = RESET BIT SELECT 0 BIT SET/RESET FLAG CONTROL WORD DON’T CARE X X X 0 = ACTIVE 1234567 01010101 00110011 00001111 B0 B1 B2 MODE 0 PORT DEFINITION A B GROUP A # GROUP B D4 D3 D1 D0 PORT A PORTC (Upper) PORT B PORTC (Lower) 0 0 0 0 Output Output 0 Output Output 0 0 0 1 Output Output 1 Output Input 0 0 1 0 Output Output 2 Input Output 0 0 1 1 Output Output 3 Input Input 0 1 0 0 Output Input 4 Output Output 0 1 0 1 Output Input 5 Output Input 0 1 1 0 Output Input 6 Input Output 0 1 1 1 Output Input 7 Input Input 1 0 0 0 Input Output 8 Output Output 1 0 0 1 Input Output 9 Output Input 1 0 1 0 Input Output 10 Input Output 1 0 1 1 Input Output 11 Input Input 1 1 0 0 Input Input 12 Output Output 1 1 0 1 Input Input 13 Output Input 1 1 1 0 Input Input 14 Input Output 1 1 1 1 Input Input 15 Input Input 82C55A |
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