' -----------------------------------------------------------------------
' DumpA.bas - Ben Ryves 2007
' -----------------------------------------------------------------------
' When run, downloads real variable 'A' off a connected TI-83 Plus, and
' transmits it (formatted as ASCII text) on the serial out pin.
' Due to space limitations (ha!) the formatting is quite crude and won't
' work at extreme levels; -99999999999999..+99999999999999 is the maximum
' range. Leading noughts are, however, handled.
' Reqires a PICAXE-08M for its 256B EEPROM.
' Many thanks to Tim Singer and Romain Liévin's TI Link Protocol Guide.

' Pinout configuration:
Symbol Data0 = 1
Symbol Data1 = 2
Symbol Data0Pin = Pin1
Symbol Data1Pin = Pin2

' Variable allocation:
Symbol BitCounter = B13
Symbol ByteToXfer = B12
Symbol CheckBit   = B11
Symbol Exponent   = B10
Symbol RangeStart = B9
Symbol RangeEnd   = B8

' Entry point:
Main:

	' Set CPU clock to 8MHz:
	SetFreq M8

	' Request variable 'A':
	RangeStart = 0 : RangeEnd = 18
	GoSub SendByteRange
	
	' Response from calculator is 23 bytes long;
	For B0 = 0 To 22
		GoSub GetByte
	Next

	' Acknowledge header and CTS:
	RangeStart = 19 : RangeEnd = 26
	GoSub SendByteRange

	' Skip first 8 bytes of response:
	For B0 = 0 To 7
		GoSub GetByte
	Next

	' Now we need to decode the data!
	
	' Real number format:
	' 1 Flags (if MSB set, it's negative).
	' 1 Exponent (+$80)
	' 7 Mantissa (Packed BCD).
	
	' Check flag byte for negative:
	GoSub GetByte
	If ByteToXfer < $80 Then IsPositive
		SerTxd ("-")
	IsPositive:

	' Grab exponent into B3:
	GoSub GetByte
	Exponent = ByteToXfer - $7F
	
	If Exponent < $80 Then PositiveExponent
		SerTxd (".")
		For B0 = Exponent To $FF
			SerTxd ("0")
		Next
	PositiveExponent:
	
	' Now, let's read the mantissa and unpack:	
	For B0 = 0 To 6
		GoSub GetByte
		BitCounter = ByteToXfer / $10
		GoSub OutPackedDigit
		BitCounter = ByteToXfer & $0F
		GoSub OutPackedDigit

	Next	
End

OutPackedDigit:
	If Exponent != 0 Then NoExponent
	SerTxd (".")
NoExponent:
	Exponent = Exponent - 1	
	SerTxd (#BitCounter)
Return

' Data

Data (%11001110, %01000101, %10110000, %00000000)
Data (%10010000, %00000000, %00000000, %10000010)
Data (%00000000, %00000000, %00000000, %00000000)
Data (%00000000, %00000000, %00000000, %00000000)
Data (%00000000, %01010010, %00000000)

Data (%11001110, %01101010, %00000000, %00000000)
Data (%11001110, %10010000, %00000000, %00000000)

' GetByte
' Receives a byte from the connected TI calculator.
' Inputs: None.
' Outputs: ByteToXfer (received byte).
' Destroys: BitCounter.

GetByte:
	ByteToXfer = 0	
	For BitCounter = 0 To 7
	
		ByteToXfer = ByteToXfer / 2

		WaitGet:
			If Data0Pin = Off Then GotBit0
			If Data1Pin = Off Then GotBit1
		GoTo WaitGet
		
	GotBit0:
		Low Data1
		If Data0Pin = Off Then GotBit0
		Input Data1
	
		GoTo GotAndUsedBit
		
	GotBit1:
		Low Data0
		ByteToXfer = ByteToXfer + $80
		If Data1Pin = Off Then GotBit1	
		Input Data0
		
	GotAndUsedBit:
	Next
Return
	
' SendByteRange
' Sends a byte range to the connected TI calculator.
' Inputs: RangeStart..RangeEnd (memory range to output).
' Outputs: None.
' Destroys: BitCounter, CheckBit.
' Remarks: Data must be stored backwards; ie, %01100001 would be stored %10000110.

SendByteRange:
	For CheckBit = RangeStart To RangeEnd
		Read CheckBit, ByteToXfer
		For BitCounter = 0 To 7
		
			If ByteToXfer >= $80 Then SendBit1
		
		SendBit0:
			Low Data0
			WaitD1L: If Data1Pin = On Then WaitD1L
			High Data0
			WaitD1H: If Data1Pin = Off Then WaitD1H
			GoTo SentBit
			
		SendBit1:
			Low Data1
			WaitD0L: If Data0Pin = On Then WaitD0L
			High Data1
			WaitD0H: if Data0Pin = Off Then WaitD0H
			
		SentBit:
			ByteToXfer = ByteToXfer * 2
			Input Data0
			Input Data1
			
		Next
	Next
Return