8253ppt
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The 8253 is a programmable timer/counter chip used in Intel microcomputers. It has 3 counters and 6 programmable modes. The modes determine how the OUT signal behaves, such as pulsing low/high periodically or non-periodically. The control byte programs the counter selection, read/write mode, count mode, and binary/BCD selection. Common uses include creating time intervals and counting events.
8253ppt
- 1. By: Masud-ul-Hasan Programmable Interval Timer 8253 (PIT) COE305 Lab.
- 2. By: Masud-ul-Hasan What is 8253? • The Intel 8253 is a programmable counter/ timer chip designed for use as an Intel microcomputer peripheral. • It is packaged in a 24-pin plastic DIP. • Six programmable timer modes allow the 8253 to be used as an event counter, elapsed time indicator, programmable one-shot, and in many other applications e.g., to create different intervals. • It has 3 counters: – Counters 0, 1, 2
- 3. By: Masud-ul-Hasan Block Diagram of 8253 •Each counter in the block diagram has 3 lines connected to it. Two of these lines, clock and gate, are inputs. The third, labeled OUT is an output. •The function of these lines changes and depends on how the device is initialized or programmed.
- 4. By: Masud-ul-Hasan Interpretation of the Timer Control Byte • Bits 7,6: Counter Selection (00 to 10) • Bits 5,4: Read/load mode for 2-byte count value: 00 -- latch count for reading 01 -- read/load high byte only 10 -- read/load low byte only 11 -- read/load low byte then high byte • Bits 3,2,1: Count mode selection (000 to 101) • Bit 0: 0/1- Count in binary/BCD
- 5. By: Masud-ul-Hasan Modes of Operation of 8253 • There are 6 modes of operation of 8253 • Differences in modes are: – “OUT” signal in different shapes like low-high or high- low, periodic or non-periodic – How to trigger/start the counter • Mode 0 and 1 are same in shape (non-periodic) • Mode 4 and 5 are same in shape (non-periodic) • Mode 2 and 3 are almost same in shape (periodic)
- 6. By: Masud-ul-Hasan Modes of Operation of 8253 • Mode 0: Set Output Bit when timer done. The output will start off zero. The count is loaded and the timer will start to count down. When the count has reached zero the output will be set high, and remain high until the next count has been reloaded. • Mode 1: Programmable One-Shot. The output will go low following the rising edge of the gate input. The counter will count and the output will go high once the counter has reached zero.
- 7. By: Masud-ul-Hasan Modes of Operation of 8253 • Mode 2: Rate Generator. The counter will continually count down, when the count reaches zero, the output will pulse low and the counter will be reloaded. • Mode 3: Square Wave Generator. This mode is similar to Mode 2 except the output remains low for half of the timer period and high for the other half of the period.
- 8. By: Masud-ul-Hasan Modes of Operation of 8253 • Mode 4: Software Triggered Pulse. The output will remain high untill the timer has counted to zero, at which point the output will pulse low and then go high again. • Mode 5: Hardware Triggered Pulse. The counter will start counting once the gate input goes high, when the counter reaches zero the output will pulse low and then go high again.
- 9. By: Masud-ul-Hasan • If 6 is loaded in the counter then it will start count down from 6 0. After reaching 0, change the OUT signal like from Lo Hi. • First 2 MSBs select the counter. Addresses for 3 counters in flight board’s 8253 are: Modes of Operation of 8253 0EHWrite OnlyControl Word 0CHRead/WriteCounter 2 0AHRead/WriteCounter 1 08HRead/WriteCounter 0 Port AddressActivity AllowedRegister
- 10. By: Masud-ul-Hasan Modes of Operation of 8253