UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

 

P12: using peripheral timer TMR2

P12

4-bit serial transmitter with LCD and TMR2 (design phase #4)

1. Specifications

This is an example of design phase #4: replace TMR0 in s_trans_LCD_TMR0 proposed in design phase #3, by the internal timer peripheral TMR2.

Symbol

Fig. 1. Project s_trans_LCD_TMR2 symbol (entity name is shortened for not reaching Windows naming length limit).

2. Planning

A) Planning hardware

The electronic schematic is the same as in design phase #3, we simply replace an internal peripheral by another, thus keeping the same hardware circuit.

Study how the TMR2 works. It has an architecture that implements a hardwired paralle load (LD) signal or synchronous reset that makes it ideal for truncated counting using an additional 8-bit comparator. No software overhead is necessary in ISR() for reinitialing the up counter TMR2 when reaching the same value stored in PR2 register.

http://digsys.upc.edu/ed/CSD/units/Ch4/U4_14/img9.jpg

Fig 2. Hardware components (a kind of RTL view) of the TMR2 of the Microchip PIC18F4520.

The key idea for our application is to geneate the same var_CLK_flag from TMR2 interrupts.

TMR2_application

Fig. 2. TMR2 configuration for generating a timing period TP = 6.666 ms. In this application, no extra software post-scaler variable N4 is required.

 

B) Planning software 

No changes in the state diagram from design phase #3. We simply have to configure and use TMR2 at the same states where we did it for TMR0.

Project location:

C:\CSD\P12\s_trans_LCD_TMR2\(files)

 

3. Developing and 4. Testing the design using EDA tools

A) Developing hardware

Our electronic circuit s_trans_LCD_TMR2.pdsprj is the same that we developed in design phase #3 becasue we simple replace internal peripheral TMR0 by TMR2.

B) Developing software

This is an example of project source code s_trans_LCD_TMR2.c where we have simply enabled, configured and used TMR2 where previously had TMR0. This project must include LCD libraries as well.

C) Step-by-step testing

We can run and debug the application using our usual resources and tools: breakpoints, step-mode, watching variables of interest, etc. For instance, Fig. 3 shows how to measure timing periods generated between TMR2 interrupts.

Running and debugging the application

Fig. 3. Measuring timing periods generated by TMR2 interrupts using breakpoints. There is an interrupt event every TP = 1μs · 4 · 119 · 14 = 6664 μs as expected.

 

5. Report

 

6. Prototyping