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- Microprocessor - Programming 8255 Mode 1 (slide 11-26 )

- Microprocessor - Programming 8255 Mode 1 (slide 11-26 ). Prepared by: Mahmoud Abdullah Mahdi 20060243 (33). Mode1 – Port A. INPUT. - Description of each pin :. Port A. - STB (PC4/PC2): The STROB input loads data into the port latch on a 0-to-1 transition . INTE (A). PC4. STB.

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- Microprocessor - Programming 8255 Mode 1 (slide 11-26 )

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  1. - Microprocessor -Programming 8255Mode 1(slide 11-26 ) Prepared by: Mahmoud Abdullah Mahdi 20060243 (33)

  2. Mode1 – Port A INPUT - Description of each pin : Port A - STB (PC4/PC2): The STROB input loads data into the port latch on a 0-to-1 transition INTE (A) PC4 STB - IFB (PC5/PC1): Input Buffer Full is an output indicating that the input latch containing information PC5 IBF - INTR (PC3/PC0): Interrupt Request is an output that request an interrupt PC3 INTR - INTE:The Interrupt Enable signal is neither an input nor an output; it is an internal bit programmed via the PC4 (port A) or PC2 (port B) PC6 & PC7 I/O - PC7 & PC6: They are general purpose I/O pins. INPUT Mode1 – Port B Port B - Important Notice : 1. Input device sends the STB. INTE (B) PC2 STB PC1 2. Input Device should not send STB, if IBF is logic ‘1’ IBF 3. INTR tells the CPU to get the data from 8255 PC0 INTR 4. CPU sends INTA, after reading data from 8255

  3. 4. CPU sends INTA, after reading data from 8255 1. Input device sends the STB. 2. Input Device should not send STB, if IBF is logic ‘1’ 3. INTR tells the CPU to get the data from 8255 Mode1 – Port A INPUT Port A Timing Diagram INTE (A) PC4 STB STB PC5 IBF PC3 INTR PC6 & PC7 I/O (Buffer Full) IBF INPUT Mode1 – Port B Port B Int. Request INTR INTE (B) PC2 STB RD PC1 IBF PC0 INTR From I/O Device Inside 8255 Inside µP

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