1, initial programming, there are two key points: to determine the control word counter count initial value to make these two accurate, programming is very simple. First determine the control word. 8253 coresThe chip has an 8-bit control word register (D7D6D5D4D3D2D1D0), where D7D6: counter (channel) selection, D5D4: counter read/write mode, D3D2D1: counter work mode, D0: count mode (binary or BCD count).
2, the second step, write the initial value of the count. The initial value of the count is written to the port address of each counter. (2) Read operation The CPU can read the counter of 8253 to read the current value of the counter. In the 8086 system, there is a piece of 8253, whose port address is assigned: channel 0For 120H, 122H for channel 1, 124H for channel 2, and 126H for the control port.
3. Read/write logic. This is the control part of 8253's internal operations. First, there is the control part of the chip selection signal CS. When CS is high, the data bus buffer is in three states, and the data bus of the system is disconnected, so it cannot be programmed or read and write operations can be performed. Secondly, this part selects the port of the read and write operation (3 counters and control word registers), and controls the direction of data transmission. Control word register.
4, After analysis, choose scheme 2 for design.In the design of Scheme 2, two main chips are used, one is the parallel interface 8255, and the other is the counter 8253. The following describes the main functions of these two devices and the functions applied in this system. 8255 Parallel interface. The 8255 is a 40-pin dual-in-line integrated circuit chip.
5, with the following basic functions: (1) there are three independent 16-bit counters. (2) Each counter can be counted in binary or decimal (BCD). (3) Each counter can be programmed to work at 6A different way of working. (4) The maximum count frequency allowed for each counter of 8254 is 10MHz (8253 is 2MHz).
is a programmable timing/counter that has three 16-bit counters that countThe frequency range is 0-2MHz, powered by a single 5V power supply. 8253 functional uses: (1) delay interruption; ⑵ Programmable frequency generator; (3) Event counter; (4) Binary Frequency multiplier (5) Real-time clock; 6 Digital single stable complex motor controller.
40H ④ asynchronous receiving mode: When 8251A works in asynchronous mode and is ready to receive a character, the low level is detected on the RxD line, and an internal counter in the receiving control circuit is started to count, when the count is carried out corresponding to half a digital transmission time, and the RxD line is detected, if at this timeStill low, a valid start bit is acknowledged.
Master: interrupt basic principle, interrupt response, timing, interrupt processing process, interrupt service programming, interrupt vector calculation; 8259A and 8253 operating principles, initialization programming, typical system application, typical schematic connection, circuit analysis, and application program design (8153 in the way of Mode 3,8259 cascades). Understand: Programmable DMA controller 8237A working principle (general principle: DMA bus application, response process).
The count constant is the key parameter used by 8253 to count. The 8253 has 3 independent counting channels and uses a minus 1 counting mode. When the gating signal is effective, the channel performs one count operation for each input of one count pulse. When the count pulse is a clock signal with a known period, the count becomes timed.
When A1A0 is 00 01 10 11, select the three channels and control word registers respectively in the 8088 system, and connect the A1A0 of 8088 to the A1A0 of 8253 in the 8086 system, usually 8253 8-bit dataThe line is connected to the lower 8 bits of the 8086, which uses even addresses, so the 8086's A2A1 is connected to the 8253's A1A0 respectively. The Intel 8253 is a programmable timer/counter chip with three separate 16-bit counter channels.
The counter 0~2 and control word port address of 8253 chip in a system are FFF0H~FFF3H respectively. Define counter 0 to operate in mode 2, CLK0=5MHz, and require OUT0=1KHz frequency wave output. Define channel 1 to work in mode 4, with OUT0 as the counting pulse, countingThe value is 1000, the counter counts to 0, sends an interrupt request signal to the CPU, connected to the PC series IRQ4.
intel8253 is a programmable counter/timer made of NMOS process, there are several chip models, shape pins and functions are compatible, but the highest count rate of work is different, such as 8253 (6MHz), 8253-5 (5MHz). The executive unit is actually a 16-bit subtraction counter whose starting value is the value of the initial value register, which is set by the program.
Intel's timer/counter is a programmable timer PIT, model 8253, and the improved model 8254, which is a circuit designed to complete the above functions. With the development of ASIC, the common 8253PIT chip in practical engineering shows the following deficiencies: the counting frequency is not enough, the 8253 count rate is up to 2MHz, and even its improved 8254 often cannot meet some projects that require higher counting frequency.
【 Answer 】 : Programmable counter and timer 8253 There are 6 working modes: (1) Mode 0 generates an interrupt for the end of the count; (2) Mode 1 is a programmable monostable trigger; (3) Mode 2 is a frequency divider; (4) Mode 3 is a square wave frequency generator; (5) Mode 4 is the software trigger strobe pulse; (6) Mode 5 is a hardware triggered strobe pulse.
Experiment 8253 square Wave experiment Objective (1) To learn the principle and method of 8253 chip and microcomputer interface. (2) Master the working mode and programming principle of 8253 timer/counter. Experimental instrument oscilloscope teaching machine Computer experiment content 8253 0 generalWorking in mode 3, generates square waves.
The experiment requires the use of 8086 external 8253 programmable timing/counter, can realize the generation of square waves. Objective To learn the connection method between 8086 and 8253. Learn the control method of 8253.
Programmable counter and timer 8253 has 6 working modes: (1) Mode 0 generates an interrupt for the end of the count; (2) Mode 1 is a programmable monostable trigger; (3) Mode 2 is a frequency divider; (4) Mode 3 is a square wave frequency generator; (5) Mode 4 is softPiece trigger gate pulse; (6) Mode 5 is a hardware triggered strobe pulse.