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WS82C55A-5Q Datasheet(PDF) 9 Page - Wing Shing Computer Components |
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WS82C55A-5Q Datasheet(HTML) 9 Page - Wing Shing Computer Components |
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9 / 25 page  9 INTR (Interrupt Request) A “high” on this output can be used to interrupt the CPU when and input device is requesting service. INTR is set by the condition: STB is a “one”, IBF is a “one” and INTE is a “one”. It is reset by the falling edge of RD. This procedure allows an input device to request service from the CPU by simply strobing its data into the port. INTE A Controlled by bit set/reset of PC4. INTE B Controlled by bit set/reset of PC2. Output Control Signal Definition (Figure 8 and 9) OBF - Output Buffer Full F/F). The OBF output will go “low” to indicate that the CPU has written data out to be specified port. This does not mean valid data is sent out of the part at this time since OBF can go true before data is available. Data is guaranteed valid at the rising edge of OBF, (See Note 1). The OBF F/F will be set by the rising edge of the WR input and reset by ACK input being low. ACK - Acknowledge Input). A “low” on this input informs the 82C55A that the data from Port A or Port B is ready to be accepted. In essence, a response from the peripheral device indicating that it is ready to accept data, (See Note 1). INTR - (Interrupt Request). A “high” on this output can be used to interrupt the CPU when an output device has accepted data transmitted by the CPU. INTR is set when ACK is a “one”, OBF is a “one” and INTE is a “one”. It is reset by the falling edge of WR. INTE A Controlled by Bit Set/Reset of PC6. INTE B Controlled by Bit Set/Reset of PC2. NOTE: 1. To strobe data into the peripheral device, the user must operate the strobe line in a hand shaking mode. The user needs to send OBF to the peripheral device, generates an ACK from the pe- ripheral device and then latch data into the peripheral device on the rising edge of OBF. FIGURE 7. MODE 1 (STROBED INPUT) tST STB INTR RD INPUT FROM IBF PERIPHERAL tSIB tSIT tPH tPS tRIT tRIB FIGURE 8. MODE 1 OUTPUT 1 D7 0 D6 1 D5 1 D4 1/0 D3 D2 D1 D0 CONTROL WORD MODE 1 (PORT A) PC7 8 ACKA PC6 PA7-PA0 OBFA INTRA PC3 PC4, PC5 2 WR PC4, PC5 1 = INPUT 0 = OUTPUT 1 D7 D6 D5 D4 D3 D2 D1 D0 CONTROL WORD MODE 1 (PORT B) PC1 8 ACKB PC2 INTE B PB7-PB0 OBFB INTRB PC0 WR 10 INTE A WS82C55A |
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