' --------------------------------------------------------------------
' TI LINK ROUTINES for the PICAXE08 SERIES - Benjamin Ryves 29.03.2005
' --------------------------------------------------------------------
' These routines are intended for use with a graphical calculator from
' Texas Instruments or compatible device. They implement the basic
' hardware link protocol - to transfer variables between devices you
' will need to implement the software link routines. These have been
' well documented by Romain Liévin and Tim Singer. Visit ticalc.org
' for links to further reading on the subject of linking. It is
' largely due so their documentation that I was able to construct link
' with the calculator at all!
'
' --------------------------------------------------------------------
' Setting up the link routines
' --------------------------------------------------------------------
' I was initially put off building a hardware link as I thought I had
' to do all sorts of strange magic with transistors and four IO pins
' on a PIC. How wrong I was! The PICAXE can gracefully switch between
' input/output modes on pins and the behavious here is perfect for the
' needs of the calculator.
' The link cable is made up of 3 leads - two data lines and a common
' grounding. The cable is tipped with 2.5mm stereo jacks.
' If you cut up a TI calc-to-calc cable, you will see that one wire is
' coloured red and the other white. Red is D0 in these routines, white
' is D1. Red is the tip of the stereo jack plug. White is the ring.
'                                          ______
'                      __   ___   ________/     /
'                     /  \_/   \_/        |     \
'                    | D0 |  D1 | GROUND  |     / 
'                    |RED |WHITE| COPPER  |     \
'                     \__/ \___/ \________|     /
'                                         \_____\
' 
' You'll need to select two of IO the pins on your PICAXE as pins to
' connect to the data lines of your TI cable. The only requirement is
' that they can switch between input and output modes. Now, you need
' to edit my code a little. You need to edit the "symbol" directives.
' Let's say that you've connected D0 to pin 3, and D1 to pin 4. The
' block would look like this:
'
'   |symbol pDATA0 = pin3
'   |symbol pDATA1 = pin4
'   |symbol nDATA0 = 3
'   |symbol nDATA1 = 4
'
' Sorry about having two "symbol" directives for each data line. I do
' not know of any other way to do it!
' Now, the last thing that needs doing is adjusting the other 3
' "symbols" (bitCounter, byteToXfer and checkBit) so that they don't
' interfere with your own variables. I gave them the last few, so
' unless you use a lot of variables I hope you don't run into them!
'
' --------------------------------------------------------------------
' Using the link routines
' --------------------------------------------------------------------
' This is very simple!
' To send a byte, load the value you want to send into "byteToXfer"
' and call the sub "sendByte" with the "gosub" instruction.
' To receive a byte, just call the sub "getByte" and the value will be
' placed into "byteToXfer".
' A simple program to test that the link works is like this:
'
'   |testLoop:
'   |     gosub getByte
'   |     gosub sendByte
'   |     goto testLoop
'
' This will get a byte then spit it right back again! If you use a
' terminal program on your calculator (such as Telnet 83, which I used
' in testing) then you should be able to type in that and watch all
' your letters being echoed back to you. Nifty, huh?
'
' --------------------------------------------------------------------
' Contacting me
' --------------------------------------------------------------------
' Shaved off a few bytes? Sped them up? Ported to another chip? Bugs?
' Or just made a really cool TI-connected device? Contact me!
' email: benryves@benryves.com
' web: http://www.benryves.com
' You also can use my email address in MSN if you want.


' ---------------------------------------
' SYMBOLS TO DEFINE IO PINS AND VARIABLES
' ---------------------------------------
symbol pDATA0 = pin1
symbol pDATA1 = pin2
symbol nDATA0 = 1
symbol nDATA1 = 2
symbol bitCounter = b11
symbol byteToXfer = b12
symbol checkBit   = b13

' Here's a really bad sample program. It sends the keypress
' kCatalog to the calculator every 10 seconds, making the
' calculator switch to the catalogue of functions.
' I had a really exciting one lined up that sent a variable
' over using the SLP but ran out of EEPROM space. I need a
' PICAXE-08M :(
	
mainLoop:

	EEPROM 0,(115,135,62,0)
	for b0 = 0 to 3
	read b0,byteToXfer
	gosub sendByte
	next
	for b0 = 0 to 7
	gosub getByte
	next
      
	pause 10000

	goto mainLoop

' End of really bad sample program
	

' ----------------------
' BYTE TRANSFER ROUTINES
' ----------------------
getByte:
	byteToXfer = 0
	for bitCounter = 0 to 7
	byteToXfer = byteToXfer / 2
waitGetBit:
	if pDATA0 = 0 then gotBit0
	if pData1 = 0 then gotBit1
	goto waitGetBit
gotBit0:
	low nDATA1
	if pDATA0 = 0 then gotBit0
	input nDATA1
	goto gotAndUsedBit
gotBit1:
	low nDATA0
	byteToXfer = byteToXfer + 128
	if pDATA1 = 0 then gotBit1	
	input nDATA0	
gotAndUsedBit:
	next
	return

sendByte:
	for bitCounter = 0 to 7
	checkBit = byteToXfer & 1
	if checkBit = 1 then sendBit1
sendBit0:
setD0L:
	low nDATA0
waitD1L:
	if pDATA1 = 1 then waitD1L
	
setD0H:
	high nDATA0
waitD1H:
	if pDATA1 = 0 then waitD1H
	goto sentBit
sendBit1:
setD1L:
	low nDATA1
waitD0L:
	if pDATA0 = 1 then waitD0L
setD1H:
	high nDATA1
waitD0H:
	if pDATA0 = 0 then waitD0H
sentBit:
	byteToXfer = byteToXfer / 2
	input nDATA0
	input nDATA1
	next
	return