We often find that there are often some mistakes in the rules or principles that we take for granted. Electronic engineers also have such examples in circuit design. The following are the eight misunderstandings that an engineer has summarized. Phenomenon 1: This board's PCB design requirements are not high, just use a thin line, automatic cloth Comments: Automated wiring must occupy a larger PCB area, and at the same time produce more than a lot of vias than manual wiring. In large batches of products, the factors considered by PCB manufacturers to cut prices are line width and The number of holes, which affect the yield of the PCB and the consumption of the drill bit, respectively, saves the cost of the supplier, and finds a reason for the price reduction. Phenomenon 2: These bus signals are pulled with resistance, feel relieved Comments: There are many reasons why the signal needs to be pulled up, but not all of them have to be pulled. The pull-down resistor pulls a simple input signal, and the current is tens of microamps or less. However, if a signal is driven, the current will reach milliamperes. The current system is usually 32 bits of address data, and there may be After the 244/245 isolated bus and other signals are pulled up, a few watts of power is consumed by these resistors. Phenomenon 3: How to deal with these unused I/O ports of CPU and FPGA? Let it be empty first, then talk about it later. Comments: If the unused I/O port is left floating, it may become an input signal of repeated oscillations due to a little interference from the outside world, and the power consumption of the MOS device basically depends on the number of times the gate circuit is flipped. If you pull it up, each pin will also have a micro-ampere current, so the best way is to set it as an output (of course, you can't connect other driven signals outside) Phenomenon 4: This FPGA has so many doors left, you can play it out. Comments: The power consumption of FGPA is proportional to the number of flip-flops used and the number of flips, so the power consumption of the same model FPGA at different times of different circuits may differ by a factor of 100. Minimizing the number of flip-flops at high speeds is the fundamental way to reduce FPGA power consumption. Phenomenon 5: The power consumption of these small chips is very low, no need to consider Comments: It is difficult to determine the power consumption of the chip that is not too complicated inside. It is mainly determined by the current on the pin. An ABT16244 consumes less than 1 mA without load, but its indicator is each foot. Can drive 60 mA load (such as matching tens of ohms of resistance), that is, the maximum power consumption of up to 60 * 16 = 960mA, of course, only the power supply current is so large, the heat is falling on the load. Phenomenon 6: There are so many control signals in the memory. I only need to use OE and WE signals on this board. The chip selection is grounded, so the data is much faster when I read the operation. Comments: Most of the memory power consumption is more than 100 times larger than when the chip select is valid (regardless of OE and WE), so CS should be used to control the chip as much as possible, and if other requirements are met, It is possible to shorten the width of the chip select pulse. Phenomenon 7: How do these signals have overshoot? As long as the match is good, it can be eliminated. Comments: Except for a few specific signals (such as 100BASE-T, CML), there are overshoots. As long as they are not very large, they do not necessarily need to match, even if the match is not the best match. The output impedance of TTL is less than 50 ohms, and some even 20 ohms. If such a large matching resistor is used, the current is very large, the power consumption is unacceptable, and the signal amplitude will be too small to be used. In addition, the output impedance of the general signal at the output high level and the output low level is not the same, and there is no way to achieve a perfect match. Therefore, the matching of signals such as TTL, LVDS, and 422 can be accepted as long as the overshoot is acceptable. Phenomenon 8: Reducing power consumption is a matter for hardware personnel, and it has nothing to do with software. Comments: The hardware is just a stage. The software is the software. The access of almost every chip on the bus and the flipping of each signal are almost controlled by software. If the software can reduce the number of external accesses (use more register variables, More use of internal CACHE, etc., timely response to interrupts (interrupts are often active low with pull-up resistors) and other specific measures for specific boards will greatly contribute to reducing power consumption.
984 controllers are available in four generic hardware classes:
Large, rugged, high-performance chassis mount controllers
Rugged, midrange-performance slot mount controllers, which reside in a
primary housing beside 800 Series I/O Modules
Host-based controllers built on various industry-standard computer cards
designed to reside in and execute control logic from a host computer
Low-cost, easy-to-install compact controllers, for applications with less
demanding environmental and performance requirements
The family approach to 984 controller design allows you to make choices based
on controller capacity (the number of discrete and analog/register points available
for application programming, the number of I/O drops it supports), throughput (the
rate at which it solves logic and updates I/O modules), and environmental hardness
(the design standards its hardware implementation must meet).
A major advantage of the family approach to 984 controller design is product
compatibility. Regardless of its computational capacity, performance characteristics,
or hardware implementation, each 984 controller is architecturally consistent
with other 984s.
The 984 instruction set (the functional capabilities of the controller, part of the system
firmware stored in executive PROM) comprises logic functions common to
other 984s. This means that user logic created on a midrange or high-performance
unit such as a 984-685 or a 984B can be relocated to a smaller controller
such as a 984-145 (assuming sufficient memory in the smaller machine) and that
logic created on a smaller controller is upwardly compatible to a larger unit. As
your application requirements increase, it is relatively easy to upgrade your controller
hardware without having to rewrite control logic.
Also, training costs and learning curves can be reduced, since users familiar with
one 984 model automatically have a strong understanding of others.
Modicon PC0984 Programmable Controller Modicon PC 0984 Programmable Controller,Communication Processor,Processor Module,CPU Module Xiamen The Anaswers Trade Co,.LTD , https://www.answersplc.com