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People's opinions are mixed on the use of Assembly to program the PIC. I like it and find it nicer than the higher level languages. The trick to assembly is to think in small steps and in patterns. |
Some while ago, back in Grad School, I discovered the PIC microcontroller. This line of chips, made by Microchip allow for projects to have that little bit of needed digital smarts in a fairly small package and cheap. They're effectively a disposable computer, the cheapest ones going for $0.50 each in bulk from online suppliers, while modestly powered ones can be had for a few bucks or less.
Now, unfortunately, other things put the interest on hold for a while, but recently I've return and am starting to make progress. So I figured I'd do some documenting. I did pick up the book Programming and Customizing PICmicro Microcontrollers (I've got the second edition) and it has a bunch of useful material.
The main chip I've been using is the pic16f777. This is a low to mid range chip with enough features to do a bunch of interesting things. It sports a bunch of I/O pins and a USART.
| SPBRG for BRGH=0 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Baud | 500 KHz | 1 MHz | 2 MHz | 4 MHz | 8 MHz | 10 MHz | 12 MHz | 16 MHz | 20 MHz |
| 300 | 25 | 51 | 103 | 207 | -- | -- | -- | -- | -- |
| 600 | 12 | 25 | 51 | 103 | 207 | -- | -- | -- | -- |
| 1,200 | -- | 12 | 25 | 51 | 103 | 130 | 155 | 207 | -- |
| 2,400 | -- | -- | 12 | 25 | 51 | 64 | 77 | 103 | 129 |
| 4,800 | -- | -- | -- | 12 | 25 | -- | 38 | 51 | 64 |
| 9,600 | -- | -- | -- | -- | 12 | -- | -- | 25 | -- |
| 14,400 | -- | -- | -- | -- | -- | -- | 12 | -- | -- |
| 19,200 | -- | -- | -- | -- | -- | -- | -- | 12 | -- |
| SPBRG for BRGH=1 | |||||||||
| Baud | 500 KHz | 1 MHz | 2 MHz | 4 MHz | 8 MHz | 10 MHz | 12 MHz | 16 MHz | 20 MHz |
|---|---|---|---|---|---|---|---|---|---|
| 1,200 | 25 | 51 | 103 | 207 | -- | -- | -- | -- | -- |
| 2,400 | 12 | 25 | 51 | 103 | 207 | -- | -- | -- | -- |
| 4,800 | -- | 12 | 25 | 51 | 103 | 129 | 155 | 207 | -- |
| 9,600 | -- | -- | 12 | 25 | 51 | 64 | 77 | 103 | 129 |
| 14,400 | -- | -- | -- | -- | 34 | 42 | 51 | 68 | 86 |
| 19,200 | -- | -- | -- | 12 | 25 | -- | 38 | 51 | 64 |
| 28,800 | -- | -- | -- | -- | -- | -- | 25 | 34 | 42 |
| 38,400 | -- | -- | -- | -- | 12 | 15 | -- | 25 | 31 |
| 57,600 | -- | -- | -- | -- | -- | -- | 12 | -- | -- |
To make it on the above charts, the computed baud rate had to be within 1% of the desired value. If one doesn't wish to bother with interoperating with other off-the-shelf devices, then the available baud rates will vary between 1,220 to 1,250,000 baud for the 20MHz device.