With the notch on an integrated circuit dual inline package facing left, where is pin 1 located?
You were given your components and your datasheet, and you’re studying to begin hacking. But in which manner does the chip go? Pin 23 is in which? If you`re lucky, the orientation is in reality marked, or possibly diagrammed withinside the datasheet. dual inline package But if it isn`t, or if you`re genuinely new at this, it`s beneficial to recognize what to search for.
In the photo above, pin 1 is marked at the Allen-Bradley resistor pack.
And for higher or worse, that is the exception, now no longer the rule. Here is a primary rule that applies to most integrated circuits: There`s a polarity mark somewhere. From that polarity mark, pass counterclockwise across the chip, and a wide variety of pins beginning at 1.
A not unusual place polarity marker is a half-moon form at one cease of the chip. Another is a small dot via way of means of pin 1, or once in a while a small triangle or tab as a substitute. Sometimes numerous of those marks can appear.
In this sketch, we`ve drawn an imaginary component wide variety
“THX1138D,” synthetic in week 37 of 2013, has a mysterious lot or inner code “OHAI” that can or might not be defined withinside the datasheet. The polarity marks are a half-moon indentation at the left-hand aspect in addition to a dot via way of means of pin 1. This tool has 20 pins, numbered counterclockwise alongside the 2 edges from 1 to 20.
As we`ll see, there are lots of examples of this, or near versions of it. But there also are instances in which there are *no* direct marks, however, you may as a substitute depending on the orientation of the textual content to recognize the numbering. The textual content orientation is consistent, and for chips of this form (with pins on contrary sides), you may reliably expect that the polarity mark is going to the left of the textual content.
Here are a few conventional and exquisite examples of chips with well-marked polarity.
These are “ceramic DIP” incorporated circuit packages, dated from the cease of 1978. Each has a molded half-moon form in addition to an extra diffused dot via way of means of pin 1.
This is a current higher-density variant with an identical design. It`s a wide, low-profile plastic package deal known as a 66-pin TSSOP (and a 128M bit DDR SDRAM, if you`re curious). The orientation is given via way of means of the half-moon form at the left-hand aspect and via way of means of the dot withinside the decreased left nook. Now, that dot looks as if it`s in the direction of pin 2 than pin 1– Again, the marker regularly labels the nook in which pin 1 lives, now no longer the character pin.
This 74HC245D “octal bus transceiver”
chip from NXP has the half-moon form at the left-hand aspect, plus a barely extra uncommon polarity marking feature. The complete front fringe of the chip– the threshold containing pin 1 –is barely beveled. And now here’s a chip that has much less of a “direct” indication of its orientations– no dot or half-moon form.
As we mentioned earlier, you may depend on the orientation of the textual content in instances like this, and consider a powerful polarity mark at the left-hand aspect of the chip. Pin 1 is at the decreased left-hand aspect. If you appearance very closely, you`ll see that there’s one extra polarity marking feature, in that this chip additionally has a barely beveled front edge.
This is a rather uncommon seven-yes-seven-pin DIP chip.
It`s a neat little solid-nation relay able to switch small hundreds on AC line voltage (0. nine A at as much as 240 VAC) from a low-voltage virtual input. Presumably, it has seven pins so you can`t place it backward. This chip additionally is based on a mixture of textual content orientation and a bevel on the aspect with pin 1.
Here`s one extra variant. There`s a broadcast bar at the left-hand aspect of this chip to behave as a polarity indicator, taking the location of the half-moon form. Here`s one which we get requested approximately pretty regularly: A 17-phase alphanumeric show. LED presentations may be quite baffling, due to the fact the pin 1 area isn’t explicitly marked, and there`s no half-moon form or different apparent polarity marker. However, the label itself is a polarity marker and it`s critical to don’t forget that.
Edit: We to start with had written down that those
who observe the label-orientation rule, however, that seems now no longer to be the case. While you`d commonly assume that the pin to the left of the label might begin at pin 1, this tool (and seemingly a few different alphanumeric/7-phase presentations) follows a conference in which pin 1 is withinside the higher left of the show– contrary to the decimal point. That`s a big “+1” for checking the datasheet!
Here`s a LED matrix shows. You can type or make out marks at the again aspect below the epoxy, so it`s tempting to search for orientation tips there, however, those sorts do commonly observe the label-orientation rule. When you orient the component such that you may study the label, the powerful polarity mark is at the left-hand aspect.
In the left photo, in which the show is upright and the label is seen,
pin 1 is below the decrease-left nook. In the proper photo, in which the label is seen however the component is upside down, pin 1 is seen at the decrease-proper hand nook. Sometimes you`ll come upon very one-of-a-kind searching chips with very apparent polarity markers. This chip from Agilent has a gold stripe at the higher MAD PCB left-hand nook. Sometimes a chip has a notched nook to suggest in which pin 1 life. The white silkscreen at the circuit board suggests an exaggerated photo of this notching, via way of means of the decrease-left nook.