What's the serial clock rate on a GPIO?

[vjcro]

Hello,

I'm quite new in programming microcontrollers.
I was wondering, if I want to make a 'clock' on a GPIO, what would be it's maximum rate? I suppose - if I put, for example: RB1=1, then RB1=0 in a loop, the clock rate will be twice the time of the execution time of the used instruction. Am I right?

The thing I would like to do is to accomplish my own simple serial communication with a FPGA. The uC would generate the serial clock on a pin and the FPGA would send the bits on a data pin.
One more question regarding this: is there a boundary regarding the serial clock rate in that kind of communication?

I would appreciate any help!
Thank you in advance.

 

[doraemon]

serial clock rate

Hello!

Basically what you want to do is bit banging.
In this case, you may consider to have a standard transmission like
SPI. If you send a clock to your fpga and get one bit per clock, then
it is exactly what SPI does. But it will take you quite a few steps for each
bit.

If you transmit a byte like this (in pseudo code):
This supposes that one bit comes on rising edge of the clock.

const char BIT[] = {
    0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01
}

uint8 receive_byte(void) {
    uint8 i;
    uint8 retval = 0;
    for(i = 0 ; i < 8 ; ++i) {
        set_clock_bit_low();
        set_clock_bit_high();
        get_data_bit();
        if(data_bit) ret_val |= BIT[i];
    }
    return retval;
}

So as you see, it will take more than twice the instructions to set and reset
the port to get some usable data.

Dora.

Hello,

I'm quite new in programming microcontrollers.
I was wondering, if I want to make a 'clock' on a GPIO, what would be it's maximum rate? I suppose - if I put, for example: RB1=1, then RB1=0 in a loop, the clock rate will be twice the time of the execution time of the used instruction. Am I right?

The thing I would like to do is to accomplish my own simple serial communication with a FPGA. The uC would generate the serial clock on a pin and the FPGA would send the bits on a data pin.
One more question regarding this: is there a boundary regarding the serial clock rate in that kind of communication?

I would appreciate any help!
Thank you in advance.