Decimus hardware fix

It was all getting too awkward. A bit of short sighted design on my part had the Nokia LCD sharing an SPI port with the motor encoders. This meant that I had to turn off the encoders to write to the LCD. While no motion information would be lost by doing this, it effectively meant that I could not, for example, have the mouse hold position while updating the display. In the end I took it all apart and patched the circuit board so that the LCD is now driven from the SPI1 port and the encoders are on the SPI2 port.


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SPI data transfers

I use SPI  on my micromouse both to talk to the Nokia graphical LCD and to talk to the LS7366 quadrature encoders. A large number of devices can be connected to the SPI data lines, MOSI and MISO. Each device needs its own select line. This all appear very simple and friendly. There is, however a potential problem due to the flexibility of the SPI configuration.


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LCD testing for Decimus

Having installed the LCD, it was time to get the code working for it. First I realised that it may not have been so clever to put the LCD on the same SPI port as the encoders. This will mean that I have to take care that the encoders are not being read when the LCD is active. Since the encoders are sampled every interrupt, it means turning them off while writing to the screen. That, in turn, means not writing to the screen while moving, or holding position. I may end up having to patch the board to put the LCD on the other SPI port. In fact, I wish I had done that in the first place as it would just share lines with the UART and I could easily switch between the UART and the SPI for writing debugging messages. Ah well, live and learn. (more…)

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Adding a timer and the graphical LCD

primus micromouse splash screenThis is a fairly big jump. With the LEDs and buttons tested, it is time to add the main graphical display, made from a Nokia cellphone display. Also, there is the main system timer event.

The simple user IO is working, and it is time to add a system timer. This will generate an interrupt every millisecond. In the final mouse a lot of work will be done in here – processing buttons, driving the LEDs, reading sensors and calculating drive signals for the motors.While that may seem a lot in a millisecond, the dsPIC used in primus can execute about 16,000 instructions in that tme and we should only need a small proportion of that time. (more…)

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