How does the code get transferred?

[HenrikOlsson]

wData is assigned a value and then you GOSUB a routine called SEND.

SEND, in turn, GOUSBs a routine called OutByte where a loop itterates thru the individual bits in wData and GOUSBs either SendOne or SendZero which puts the state of the bit on the pin aliased as Sda, which in your code is PortC.5, not PortC.3.

/Henrik

[Ramius]

You are right about it being PortC.5, my oops, just not seeing where it is PortC.5 and not some other Port.

[HenrikOlsson]

Cut'n'paste from your program, relevant parts marked with red.

Pin aliases:

Clk VAR PORTC.4
 Sda VAR PORTC.5
 Csn VAR PORTC.3

Variable assignment and call to Send routine:

WData = $1877: GOSUB Send

Send routine, calls OutByte:

Send:
 GOSUB StartCommunication
 GOSUB OutByte
 GOSUB StopCommunication
 RETURN

Outbyte iterates thru wData and calls either SendOne or SendZero depending on if the bit is a one or a zero:

OutByte: 'send a 16 bit word
 FOR Bit_Counter = 1 TO 16
 IF wData.15 = 1 THEN 'MSB first
 GOSUB SendOne
 ELSE
 GOSUB SendZero
 ENDIF
 WData = wData << 1
 NEXT Bit_Counter
 RETURN

Sendone:

SendOne: 'Send a bit 0
 HIGH Sda: GOSUB WasteTime
 LOW Clk: GOSUB WasteTime
 HIGH Clk: GOSUB WasteTime
 RETURN

Sendzero:

 SendZero: 'sending a bit 1
 LOW Sda: GOSUB WasteTime
 LOW Clk: GOSUB WasteTime
 HIGH Clk: GOSUB WasteTime
 HIGH Sda: GOSUB WasteTime
 RETURN

/Henrik.