PIC Tutorial Main Board Two

Main Board Two

This is the circuit of the second main board for the tutorials, it consists of the PIC16F876, a 7805 regulator, a 20MHz crystal, 5 capacitors, three ten pin connectors, one for PortA, one for PortB, and one for PortC . Each of the three ten pin connectors is wired identically, with a ground connection at the left side, and a 5V connection at the right - this will allow you to plug the same extension board into any port, and help to demonstrate their differences - the most obvious difference is that PortA only has 6 I/O lines, which can be either digital I/O or analogue inputs, with 10 bit resolution.

Basically it's very similar to the 16F628 tutorial board, but has an extra port and added facilities - as the 16F876 doesn't have an internal oscillator a crystal is required for the clock oscillator - I choose a 20MHz crystal for this, if you can't get a 20MHz chip the 4MHz 16F876's seem perfectly happy to run at 20MHz - I suspect they are exactly the same chip, and graded to provide the two different versions.

This is a photo of the main board, it's built on a piece of Veroboard 34 strips wide, by 34 holes high. The left of the three white connectors at the bottom is PortC, the right one is PortA, and the middle one PortB (I stuck little labels on them as I keep forgetting which is which). All the wire jumpers are required to line the connectors up neatly. In order to prevent the pins of the PIC getting damaged, the PIC is permanently inserted in a 'turned pin' socket, this is then plugged into a normal socket on the board. To program it the PIC, complete with turned pin socket, is unplugged and inserted in the programmer, programmed and then returned. This is very easy to do, and the 'turned pin' socket prevents any damage. The PIC is capable of being programmed in-circuit, but it adds circuit complications and uses up I/O pins, so I haven't implemented that.
This is a bottom view of the board, I've indicated the track cuts (20 of them) with blue circles, with this picture, and the one above, it should be fairly easy to duplicate the board - remember - there are 20 track cuts, and 20 wire links.

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