Differences

This shows you the differences between two versions of the page.

--- pic24f [2019/02/28 18:58]
paul created
+++ pic24f [2019/03/31 14:50] (current)
@@ Line 1: / Line 1: @@
-====== PIC24 ======
+====== PIC24F ======
+The PIC24F is a versital microprocessor with lots of nice peripherals such as
+DAC, multiple UARTS and PWM. I used it for the [[ltp_lidar|LTP Lidar]].
+===== Documentation Notes =====
+The PIC24 from Microchip has two types of documentation. The first is the device
+specific datasheet and the second is a general set of documentation for the PIC24
+family of chips. Sometimes, especially when looking for a detailed explanation of how
+a peripheral works, the general family documentation is more helpful.
+===== General =====
+Every project has ''%%<xc.h>%%'' includes. In it there are a bunch of
+''%%ifdefs%%'' that include your device specific header. Search for it and you will find it!
+There used to be compiler libraries for the peripherals of the  PIC24 but they
+have become depracated
+(([[http://www.microchip.com/SWLibraryWeb/product.aspx?product=PIC24%20MCU%20dsPIC%20Peripheral%20Lib|Legacy
+PIC24 MCU & dsPIC DSC Peripheral Library]])). Instead perhiphal functions are
+generated by MCC (MPLAB Code Configurator).  Here is great website with info on
+I2C and the MCC I2C commands
+[[http://www.studentcompanion.co.za/interfacing-the-ds1307-real-time-clock-with-pic-microcontroller-xc8/|link]].
+===== Delay =====
+You can use the delay functions of the xc16 compiler but you have to define the
+following before including the right header file. It is this:
+<code c>
+#define FOSC    (32000000ULL)
+#define FCY     (FOSC/2)
+#include <libpic30.h>
+</code>
+Then you can use:
+<code c>
+__delay_us()
+__delay_ms()
+</code>
+===== PWM =====
+Getting PWM to work on the PIC24 is tricky. We make use of the ''%%MCCP/SCCP%%'' peripheral
+that has a tremendous amount of functionality which also makes it tricky to use.
+==== Capture/Compare/PWM/Timer Modules (MCCP and SCCP) ====
+The PIC24 has a periphal group called the ''%%MCCP%%'' and ''%%SCCP%%''. The
+data sheet here has specific register information
+[[http://www.mouser.com/ds/2/268/33030a-254597.pdf|link]].
+This document gives a detailed description of this peripheral group [[http://ww1.microchip.com/downloads/en/DeviceDoc/33035a.pdf|link]].
+Go to Section 64.7 of the PIC24 Family document.
+To make a simple PWM signal use the ''%%MCCP%%'' module in output compare with
+**Dual Edge Mode**. The **Dual Edge Mode** allows us to reset the ''%%OC%%'' (output compare) pin, set the
+pulse width and along with the 16 bit timer length.
+We use dual edge buffered ''%%MCCP1%%'' mode to generate our PWM signal. The
+buffered part is that so that we can update the PWM values while the PWM is
+running, and the peripheral takes care of loading the next values at the end of
+a cycle.
+===== SPI =====
+I learned a lot about SPI in the LTP Lidar project because it didn't work right
+off the bat. It is not that complicated and the easy setup in MCC (MPLAB Code
+Configurator) gives you all the stuff you need. You just use the
+''%%MSSP1_SPI_Exchange8bit(address)%%'' function to read and write data.
+Some notes:
+  * Make sure you have the SPI mode selected correctly!!
+  * Always break out the SPI bus SCK, MISO, MOSI and SS pins to probe test points [[https://datasheet.octopart.com/5117-Keystone-datasheet-15716159.pdf|link]] in new designs.
+===== UART =====
+To use the UART you can set it up on the the MCC (MPLAB Code Configurator).
+Check the box that diverts ''%%printf%%'' to the UART. This allows us to use
+''%%printf%%'' which can print out strings and is easier to use than the one
+byte function we get from the configurator.
+To use ''%%printf%%'' we need to ''%%#include <stdio.h>%%''
+Read about the xc16 ''%%printf%%'' implmementation [[http://microchip.wikidot.com/tls2101:printf|link]].
+To use the MCC generated ''%%UARTx_GetStatus()%%'' function you have to
+''%%AND%%'' the enum! They are flags and not unique values. So tricky!!!
+The PIC24F only has a 4 byte serial buffer. Getting the pic to do a serial read
+requires me to get out of my comfort zone and work with interrupts. I need to set up
+an interrupt every time there is a byte and add it to my running buffer. This really
+shouldn't be that hard and should make the code work pretty easily.
+I need to set the ''%%URXISEL<1:0>%%'' to ''%%00%%'' which will generate an interrupt whenever there
+is 1 or more characters in the buffer.
+There is information about the UART in both the PIC24F Family Reference manual and also
+the PIC24FV16KM204 Family Reference Manual [[https://www.digikey.com/eewiki/display/microcontroller/Microchip+PIC+Family+Reference+Manuals+-+Compiled|link]].
+This is all forcing me to learn about interrupt functions. Reading about it in
+Chapter 7 of the C30 Compiler User's Guide [[http://ww1.microchip.com/downloads/en/devicedoc/c30_users_guide_51284f.pdf|link]].
+I think I can use a macro for the UART Rx interrupt. See Section 8.3.4 in the
+Interrupts manual
+[[http://ww1.microchip.com/downloads/en/devicedoc/39707a.pdf|link]].
+Im trying to find the correct preproccessor macro for the ISR of the UARTRx
+interrupt. In doing so, I read this in the C Compiler Manual:
+<code>
+If an interrupt handler does not require any of the optional parameters of the
+interrupt attribute, then a simplified syntax may be used. The
+following macros are defined in the device-specific header files:
+</code>
+I found out I can just use the autogenerated UART handler instead of writing my
+own ISR. Which may be worse than writing my own ISR because there is a lot of
+bullshit with it.