Every first bit lost by shift out a byte to a LCD with SPI-Interface ??

tdus

Hi,

I am a Propeller fan from germany.

My question is:
By shift out a byte to the lcd every first bit is lost?
when I shift left before I send it works, but i dont understand this.

PRI SPI_Write(lcddata)        ''serial send to lcd

  lcddata <<=1                  '<-----  why I must do this ??? without this every first bit is lost
  
  repeat 8                                     'send 8 bits to the lc-display
    waitcnt(cnt += spi_timing)                 '100us wait
    outa[noparse][[/noparse]SDC] := 1                             'clock goes high
    outa[noparse][[/noparse]SDO] := (lcddata >>= 1) & 1           'Shift the bit to the SDO Pin
    waitcnt(cnt += spi_timing)                 '100us wait
    outa[noparse][[/noparse]SDC] := 0                             'clock goes low and write the bit 

The complete code (if you need) is on my Propellerpage on www.tdus.de


Thanks
Uwe

Mike Green

You have to shift lcddata left initially because the "(lcddata >>= 1) & 1" shifts the data to the right before it uses the low order bit. What you are doing is fine. If you want to avoid the initial shift, you must separate the use of the bit and the shift as follows:

repeat 8
  waitcnt(clkfreq / 10000 + cnt)   'Wait for 100us
  outa[noparse][[/noparse]SDC]~~    ' clock goes high
  outa[noparse][[/noparse]SDO] := lcddata
  lcddata >>= 1
  waitcnt(clkfreq / 10000 + cnt) 'Wait for 100us
  outa[noparse][[/noparse]SDC]~  'clock goes low

tdus

o.k. is clear as daylight.

Thank you very much