Programmable Interval Timer or – Free download as Powerpoint Presentation .ppt), PDF File .pdf), Text Programmable Peripheral Interface. Microprocessor | programmable interval timer peripheral interface) · Control Word and Operating modes · Programmable peripheral interface The Intel is a counter timer device designed to solve the common timing control problems in The is a programmable interval timer counter designed.

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We think you have liked this presentation. If you wish to download it, please recommend it to your friends in any social system. Share buttons are a little bit lower. Published by Matthew Bryant Modified over 3 years ago. The solves one of the most common problems in any microcomputer system, the generation of ac- curate time delays under software control.

Instead of setting up timing loops in systems software, the programmer configures the to match his requirements, initializes one of the counters of the with the desired quantity, then upon command the will count out the delay and interrupt the CPU when it has completed its tasks.

It is easy to see that the software overhead is minimal and tumer multiple delays can easily be maintained by assignment of priority levels.

Intel 8253 – Programmable Interval Timer

D Bidirectional Data Bus: Data transfer with the CPU is enabled when programmabel pin is at low level. When at high level, the data bus D0 thru D7 is switched to high impedance state where neither writing nor reading can be executed.

Internal registers, pgogrammable, remain unchanged. Data can be transferred from the to CPU when this pin is at low level. Data can be transferred from CPU to when this pin is at low level. These two pins are normally connected to the two lower order bits of the address bus.

Supply of three clock signals to the three counters incorporated in Control of starting, interruption, and restarting of counting in the three respective counters in accordance with the set control word contents. Output of counter output waveform in accordance with the set mode and count value. Pin configuration of the Pin description of the The 3-state, bi-directional, 8-bit buffer is used to interface the to the system data bus.


The Data Bus Buffer has three basic functions. It then accepts information from the data bus buffer and stores it in a register. The information stored in this register controls the operation MODE of each counter, selection of binary or BCD counting and the loading of each count register.

The Control Word Register can only be written into; no read operation of its contents is available.

These three functional blocks are identical in operation so only a single counter will be described. Also, there are special features in the control word that handle timed loading of the count value so that software overhead can be minimized for these functions. The reading of the contents of each counter is available to the programmer with simple READ operations for event counting applications and special commands and logic are included in the so that the contents of each counter can be read “on the fly” without having to inhibit the clock input.

Block diagram of the Description of basic operations of the Or it can be connected to the output of a decoder, such as an Intel for larger systems. System Interfacing of the Show how to interface the to the low byte of the D0-D7. Circuit interface of the in Example 1. A set of control words must be sent out by the CPU to initialize each counter of the with the desired MODE progrrammable quantity information.

Prior to initialization, the MODE, count and output of all counters is undefined.

Intel Programmable Interval Timer

Once programmed, the is ready to perform whatever timing tasks it is assigned to accomplish. A program intending to use the must provide the following sequence of actions: Select the desired counter as shown in Table 3.

Specify the operation mode of the as shown in Table 5. Format of the Control Word of the Selection of set counter in the Operation waveform mode setting in the Operation count setting in the Program the shown in the next figure according to the following settings: Circuit interface of Example 2. In this mode, the counter will start counting from the initial COUNT value loaded into it, down to 0.

Counting rate is equal to the input clock frequency. OUT will remain high until the counter is reloaded or the Control Word is written. The Gate signal should remain active high for normal counting.


If Gate goes low counting get terminated and current count is latched till Gate pulse goes high again. Illustration of Mode 0 operation. OUT will be initially high. OUT will go low on the CLK pulse following a trigger to begin the one-shot pulse, and will remain low until the Counter reaches zero.

After writing the Control Word and initial count, the Counter is armed.

The one-shot pulse can be repeated without rewriting the same count into the counter. If a new count is written to the Counter during a one-shot pulse, the current one-shot is not affected unless the counter is retriggered.

In that case, the Counter is loaded with the new count and the one-shot pulse continues until the new count expires. Illustration of Mode 1 operation. OUT will then remain high until the counter reaches 1, and will go low for one clock pulse. OUT will then go high again, and the whole process repeats itself. The time between the high pulses depends on the preset count in the counter’s register, and is calculated using the following formula: Illustration of Mode 2 operation.

However, the duration of the high and low clock pulses of the output will be different from mode 2. Illustration of Mode 3 operation. The counter will then generate a low pulse for 1 clock cycle a strobe — after that the output will become high again.

Illustration of Mode 4 operation. However, the counting process is triggered by the GATE input. Once the device detects a rising edge on the GATE input, it will start counting. When the counter reaches 0, the output will go low for one clock cycle — after that it will become high again, to repeat the cycle on the next rising edge of GATE.

Illustration of Mode 5 operation. My presentations Profile Feedback Log out. Auth with social network: Registration Forgot your password?

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