Reading the resistance value of a resistor array
In a three-digit resistance value, the first and second digits from left to right are significant figures, and the third digit represents the first two digits multiplied by 10 to the power of N (in Ω). If the resistance value contains a decimal point, it is represented by "R" and occupies one significant figure. For example: a resistance value marked "103" is 10 × 10 = 10kΩ; a resistance value marked "222" is 2200Ω, or 2.2kΩ; and a resistance value marked "105" is 1MΩ.
It is important to note that this marking method should be distinguished from the general numerical representation method. For example, a resistor marked as 220 has a resistance of 22Ω, while only a resistor marked as 221 has a resistance of 220Ω.
A resistor array marked with "0" or "000" has a resistance value of 0Ω. This type of resistor array is actually a jumper (short circuit).
Some precision resistor arrays use a four-digit number followed by a letter (or just four digits). The first three digits represent the hundreds, tens, and units digits of the resistance value, respectively. The fourth digit represents the first three digits multiplied by 10 to the power of N, in ohms. The first letter after the digits represents the tolerance (G=2%, F=1%, D=0.25%, B=0.1%, A or W=0.05%, Q=0.02%, T=0.01%, V=0.005%). For example, a resistor array marked "2341" has a resistance of 234 × 10 = 2340 Ω.
The function of resistance removal
The "sesame seeds" evenly distributed beneath the memory chip are actually "resistors arrays" located between the memory chip and the gold fingers. A resistor array is simply a row of resistors.
We know that memory generates varying amounts of operating current when processing and transmitting data. Installing a row of resistors along the necessary path of the memory chip's traces helps stabilize the voltage, making the memory operate more stably. This improves memory stability and extends its lifespan.
The "little green bean" on the right corner of the memory module you mentioned is generally called an SPD (Special Partition Diameter). An SPD is a storage device that stores detailed configuration information about the memory from the manufacturer, such as operating voltage, bit width, and timings. During each power-on self-test, the system first reads the relevant information from the SPD to automatically configure hardware resources and prevent errors. Pull-ups and current limiters, like ordinary resistors, simplify PCB design and installation, reduce space requirements, and ensure soldering quality.
Resistor pin description
The resistors between pins 1 and a2, b3, c4, and d are all 10 ohms and have no relation to the other pins. It's just a row of resistors integrated into a single component.
Some also have a male pin, which is for ease of use. If you measure it with a multimeter, you will find that the resistance of all pins to the common pin is the nominal value, and the resistance of any two other pins is twice the nominal value. Obviously, any two pins are connected in series through the common pin! It is particularly convenient to use in situations with many pull-up and pull-down resistors, such as parallel communication lines, and it also saves space.
51 microcontroller minimum system resistor elimination function
It has an upward pulling effect:
A pull-up resistor clamps an uncertain signal to a high level through a resistor, which also limits current. The same principle applies to a pull-down resistor. Pull-up injects current into a device, while pull-down outputs current. The difference between strong and weak pull-up resistors is simply the resistance value; there's no strict distinction. For non-open-collector (or open-drain) output circuits (such as ordinary gate circuits), the ability to boost current and voltage is limited. The primary function of a pull-up resistor is to provide a current path for open-collector output circuits.
In addition, all other I/O ports are quasi-bidirectional ports and have driving capabilities. Port P0 is also a quasi-bidirectional port, but its driving capability is small. Adding a resistor array is simply adding a driving circuit to P0. The power supply provides power to port P0 through the resistor array, enabling it to drive the components connected to port P0.
Soldering method for resistor arrays in microcontrollers
First, locate the common terminal of the resistor array. The common terminal is on the side of the resistor array marked with a small white dot. Alternatively, you can use a multimeter in resistance mode to measure the resistance between any one terminal and the other pins. If the resistances of all pins are equal, that terminal is the common terminal; otherwise, the other terminal is the common terminal.
The common pin connects to the microcontroller's power supply, and the other pins connect to the microcontroller's I/O ports. The soldering method is the same as for ordinary resistors, only with more pins. You can solder the two ends first, position them, and then solder the middle pin.
As shown in the figure: the dotted end is the common terminal of the resistor array.
RP is a resistor array, and J0 is connected to the segment code of the digital display. With the side of the resistor array containing the characters facing you, the leftmost pin with a dot (round or square) is the common pin.
