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MC33298 bảng dữ liệu(PDF) 14 Page - Freescale Semiconductor, Inc |
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MC33298 bảng dữ liệu(HTML) 14 Page - Freescale Semiconductor, Inc |
14 / 28 page Analog Integrated Circuit Device Data 14 Freescale Semiconductor 33298 FUNCTIONAL DESCRIPTION INTRODUCTION Figure 14. 33298 SPI System Daisy Chain One main advantage of the 33298 is the serial port. When coupled to an MCU, it receives ON/OFF commands from the MCU and in return transmits the drain status of the device’s output switches. Many devices can be daisy-chained together, forming a larger system, illustrated in Figure 14. Note In this example, only one dedicated MCU parallel port (aside from the required SPI) is required for chip select to control 32 possible loads. Multiple 33298 devices can also be controlled in a parallel input fashion using the SPI, illustrated in Figure 15. This figure shows a possible 24 loads being controlled by only three dedicated parallel MCU ports used for chip select. Figure 15. Parallel Input SPI Control Figure 16 illustrates a basic method of controlling multiple 33298 devices using two MCUs. A system can have only one master MCU at any given instant of time and one or more slave MCUs. Master control of the system must pass from one MCU to the other in an orderly manner. The master MCU supplies the system clock signal (top MCU designated the master); the lower MCU being the slave. It is possible to have a system with more than one master; however, not at the same time. Only when the master is not communicating can a slave assume the mastership and communicate. MCU master control is switched through the use of the slave select (SS) pin of the MCUs. A master will become a slave when it detects a logic low state on its SS pin. These basic examples make the 33298 very attractive for applications where a large number of loads require efficient control. To this end, the popular Synchronous Serial Peripheral Interface (SPI) protocol is incorporated to communicate efficiently with the MCU. SPI SYSTEM ATTRIBUTES The SPI system is flexible enough to communicate directly with numerous standard peripherals and MCUs available from Freescale Semiconductor and other semiconductor manufacturers. SPI reduces the number of pins necessary for input/output (I/O) on the 33298. It also offers an easy means of expanding the I/O function using few MCU pins. The SPI system of communication consists of the MCU transmitting, in return it receives one data-bit of information per system clock cycle. Data-bits of information are simultaneously transmitted by one pin, Microcontroller Out Serial In (MOSI), and received by another pin, Microcontroller In Serial Out (MISO), of the MCU. Some features of the SPI are: • Full duplex, three-wire synchronous data transfer • Each microcontroller can be a master or a slave • Provides write collision flag protection • Provides end of message interrupt flag • Four I/Os associated with SPI (MOSI, MISO, SCLK, SS) Drawbacks to SPI are: • An MCU is required for efficient operational control • In contrast to parallel input control it Is slower at performing pulse width modulating (PWM) functions. SCLK Parallel Port MISO MOSI IRQ MC68XX Microcontroller SPI SO SO SO SO CS CS CS CS SCLK SCLK SCLK SCLK SI SI SI SI 33298 33298 33298 33298 8 Outputs 8 Outputs 8 Outputs 8 Outputs 8 Outputs 8 Outputs 8 Outputs A B C Parallel Ports MC68XX Microcontroller SPI SI SCLK CS SI SCLK CS SI SCLK CS 33298 33298 33298 SCLK MOSI |
Số phần tương tự - MC33298_08 |
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Mô tả tương tự - MC33298_08 |
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