Mohammed Al-Amin

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4 years, 5 months ago.

Understanding the Physical Pins of a PortOut

Hiya Everyone!

I was working on the example of the UniGraphics code while using the ST7565 initialization as parallel 8 bit, but I'm unfortunately new to coding but trying to understand how the PortC identification works?

include the mbed library with this snippet

ST7565 myLCD(PAR_8, PortC, PA_8, PA_9, PB_10, PB_4, PB_5,"myLCD", 128, 64); // Parallel 8bit, Port, CS, reset, A0, WR, RD

Does this mean that when PortC is identified (I am using a STM32-F401RE Nucleo Board), that all of the hardware pins named PC_X are identified?

For my LCD display I have, D0 to D7 and I have connected them directly from PC_0 to PC_7, does that mean I have connected them up correctly?

The link to the code is: https://os.mbed.com/teams/GraphicsDisplay/code/UniGraphic/

Help would be much appreciated.

Best regards

Mo

1 Answer

Desmond Chen
4 years, 5 months ago.

Hi Mohammed,

PortC is defined as an enum and used to enabled GPIO clock and get GPIO base address, please look here.

https://github.com/ARMmbed/mbed-os/blob/18d4adf04f50de2452d7686b77da375881f5811b/targets/TARGET_STM/gpio_api.c#L39

Regards, Desmond

Accepted Answer

So if it enables the GPIO clock and get the GPIO base address, what makes the code identify the pins PC_0 to PC_7.

I have seen on the protocols file in PAR_8.cpp

code named:

PAR8::PAR8(PortName port, PinName CS, PinName reset, PinName DC, PinName WR, PinName RD)
    : _port(port,0xFF), _CS(CS), _reset(reset), _DC(DC), _WR(WR), _RD(RD)

Is the 0xFF value mean the assignment of the first 8 pins of portC?

If not I may still have not fully understood how programming to physical pins links work.

Best regards

Mo

posted by Mohammed Al-Amin 05 Nov 2019

Hello Mo,

The _port data member of PAR8 class is a PortInOut object:

PAR8.h

class PAR8 : public Protocols
{
    ...

private:

    PortInOut _port;
    ...
}

The _port data member is initialized in PAR8's constructor by calling PortInOut's constructor with two parameters:

    : _port(port,0xFF),

The first one selects the port to connect to.
The second parameter is a bitmask to identify which bits in the port should be included:

  • 0 - do not include
  • 1 - include
    Hence, passing 0xFF (= 0b11111111) as bitmask will include bit (physically a pin) 0, 1, 2, 3, 4, 5, 6 and 7 of the selected port into the _port PortInOut object.
posted by Zoltan Hudak 05 Nov 2019