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WS82C55AP 数据表(PDF) 13 Page - Wing Shing Computer Components |
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WS82C55AP 数据表(HTML) 13 Page - Wing Shing Computer Components |
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13 / 25 page ![]() 13 Special Mode Combination Considerations There are several combinations of modes possible. For any combination, some or all of Port C lines are used for control or status. The remaining bits are either inputs or outputs as defined by a “Set Mode” command. During a read of Port C, the state of all the Port C lines, except the ACK and STB lines, will be placed on the data bus. In place of the ACK and STB line states, flag status will appear on the data bus in the PC2, PC4, and PC6 bit positions as illustrated by Figure 17. Through a “Write Port C” command, only the Port C pins programmed as outputs in a Mode 0 group can be written. No other pins can be affected by a “Write Port C” command, nor can the interrupt enable flags be accessed. To write to any Port C output programmed as an output in Mode 1 group or to change an interrupt enable flag, the “Set/Reset Port C Bit” command must be used. With a “Set/Reset Port Cea Bit” command, any Port C line programmed as an output (including IBF and OBF) can be written, or an interrupt enable flag can be either set or reset. Port C lines programmed as inputs, including ACK and STB lines, associated with Port C fare not affected by a “Set/Reset Port C Bit” command. Writing to the correspond- ing Port C bit positions of the ACK and STB lines with the “Set Reset Port C Bit” command will affect the Group A and Group B interrupt enable flags, as illustrated in Figure 17. Current Drive Capability Any output on Port A, B or C can sink or source 2.5mA. This feature allows the 82C55A to directly drive Darlington type drivers and high-voltage displays that require such sink or source current. MODE DEFINITION SUMMARY MODE 0 MODE 1 MODE 2 IN OUT IN OUT GROUP A ONLY PA0 PA1 PA2 PA3 PA4 PA5 PA6 PA7 In In In In In In In In Out Out Out Out Out Out Out Out In In In In In In In In Out Out Out Out Out Out Out Out PB0 PB1 PB2 PB3 PB4 PB5 PB6 PB7 In In In In In In In In Out Out Out Out Out Out Out Out In In In In In In In In Out Out Out Out Out Out Out Out PC0 PC1 PC2 PC3 PC4 PC5 PC6 PC7 In In In In In In In In Out Out Out Out Out Out Out Out INTRB IBFB STBB INTRA STBA IBFA I/O I/O INTRB OBFB ACKB INTRA I/O I/O ACKA OBFA I/O I/O I/O INTRA STBA IBFA ACKA OBFA Mode 0 or Mode 1 Only INPUT CONFIGURATION D7 D6 D5 D4 D3 D2 D1 D0 I/O I/O IBFA INTEA INTRA INTEB IBFB INTRB OUTPUT CONFIGURATION D7 D6 D5 D4 D3 D2 D1 D0 OBFA INTEA I/O I/O INTRA INTEB OBFB INTRB FIGURE 15. MODE 1 STATUS WORD FORMAT D7 D6 D5 D4 D3 D2 D1 D0 OBFA INTE1 IBFA INTE2 INTRA X X X (Defined by Mode 0 or Mode 1 Selection) FIGURE 16. MODE 2 STATUS WORD FORMAT GROUP A GROUP B GROUP A GROUP B GROUP A GROUP B WS82C55A |
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