ShiftOut. Using PIC as Slave device.

Hi,

I not sure if this is possible, since I am confused about shiftout command.

I would like to use the pic as a slave device. The pic would receive the clock signal from a master device, and the pic would shift out a byte.

The master device sends the latch and clock data, the pic would receive that data and shift out a byte of serial data. Is this possible?

Thanks for any help.
TonyA

I am not sure either... Never used the PIC as a slave.

If the master device could send a signal to the PIC letting the PIC know data is ready then maybe the PIC could start a SHIFTIN ?

What is the master device?

Thanks. Well my problem is that I might not fully understand the shiftout command.

The master is another microcontroller, the Atmega8. The Atmega is sending a clock signal and latch data, the pic (slave device) will receive the clock signal and latch data, and then send out a byte of data to the Atmega.

So I'm guessing that I would just connect the clock output of the master (Atmega) to an input pin of the pic (slave) and that would be the clockpin of the command: shiftout dataOutpin, clockpin, (serial data)

The latch output signal of the master (Atmega) would be received by an input pin of the pic (latchReceivePin), and I guess I would do something like this?

If latchReceivePin = 1 then 'if the pic receives a "high" signal on its input pin then shift out a byte of data to the Atmega.
shiftout, etc.

I still don't know if I understand "shiftout" correctly, but I'll experiment with this today. If anyone can offer any advice or clues please let me know.

Thanks again.

Something like this should work (untested). Note that is "blocking", and that the code will not advance past this until you get 8 high-to-low transitions on the clock.

Code:

---

GetNextByte:

BitCounter = 0
GetNextBit:
  While ClockPin=1:Wend                ; Sits here and does nothing while clock pin is high
    DataByt.0 = DataPin                ; Samples data pin as soon as clock goes low
    BitCounter = BitCounter + 1        ; Keeps track of number of bits received
    If BitCounter = 8 then goto GotByte ; When we have a byte, get out
    DataByt = DataByt << 1              ; Move things over for next bit
  WHILE ClockPin=0:WEND                ; Sit here while clock is low
    Goto GetNextBit                    ; Grab next bit if we haven't got all 8
   
GotByte:
...
...
...
 END

---

Thank you for the help and advice, I appreciate it.

Tony A