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Free Forming the 44-pin PLCC Socket
DO NOT FREE-FORM THIS CIRCUIT WITH THE CHIP IN THE PLCC SOCKET.
One of my old employers closed down their operation, and all us poor contractors had our contracts terminated. This meant the skip at work was very full of all the electronic bits and pieces they no longer wanted. So I helped myself to them (you can now picture me, in the rain head in a skip and my legs waving in the air!)
The most useful items I got were about 30 AT89C52 Chips. These are in a PLCC configuration, so I can't use my beloved strip-board for making circuits. I had to think another way of getting them going. I ended up using a PLCC socket with the through mount holes, so the pins are far enough apart to get a soldering iron tip to them. I then rigged up the PLCC socket with the chip facing down and the pins in the air.
The schematic for this basic circuit is below and works very well. The AT89C52 is a great little chip, if your program is small enough to fit on the chip, you get a double bonus, the first is that this circuit is all you need to make it run, and the second is that you get to use ALL the I/O lines for sensors, motor drivers etc. as you're not using any external program memory.
The Schematic
Here's the schematic, note I have coloured the P1 and P3 pins so you know where they are.
The Chip needs:-
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1 5v Regulated supply
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1 ground connection
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1 10uf Capacitor
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2 33pf Capacitors
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1 Crystal (the speed depends on your chip)
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1 10K or 47K resistor
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The 5v supply goes to pin 44 (VCC)
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The ground is connected to pin 22 (GND)
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The resistor goes from pin 44 (VCC) to pin 35 (EA/VPP)
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The 10uf Capacitor goes from pin 10 (RST) to pin 44 (VCC) - make sure you put the negative side to pin 10 (RST)
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One 33pf Capacitor connected between pin 21 (XTAL1) and pin 22 (GND)
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One 33pf Capacitor connected between pin 20 (XTAL2) and pin 22 (GND)
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The Crystal is placed between pins 21(XTAL1) and 22(XTAL2)
Why?
You need power, the first two are power connections. The resistor powers the EA/VPP pin, this is the External Enable pin, if it is not powered then the I/O lines on p0 and p2 can't be used, and/or the chip will try to access External Memory to run from. Connecting this to the +5v makes the chip use it's Flash Memory for the program.
The 10uf Capacitor is used to hold the reset line high, however, we don't want it to do that straight away, because the power to the system needs to stabilise first. By using a 10uf Capacitor here we get a delay between power on and the chip starting. (we're talking nanoseconds here but that is long enough) when the pin is pulled high by the capacitor being fully charged the chip resets, and starts running. You can us a bigger capacitor here, but not a smaller one. Some recommend using a resistor - to slow down the charging of the capacitor - I assume, but I didn't find it needed one. If you are using a similar but not identical chip, you might need one. If so then connect a 10K resistor between pin pin 10(RST) and pin 22(GND). This will slow the charging of the capacitor down so the power had time to stabalise.
I'm using a crystal on my systems so I need 2 33pf capacitors between 21(XTAL1) and 20(XTAL2), if you use a ceramic resonator, you won't need them. Just connect the resonator directly to pin 21(XTAL1) and 20(XTAL2), the middle pin goes to 22(GND). if your resonator doesn't have a middle pin, there is no need to connect it to GND (obviously).
The crystal generates the clock cycles for the processor. The schematic below shows you the connections. The PLCC socket is facing down with the pins in the air, the chamfered corner is Top-Right.
Here's a really shoddy picture of a completed one.
Any questions?
You can contact me
here
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