DIM Storage$
DIM MessageLength

OPEN "COM1: 57600, 256, SerialInt, 1, INV" AS #5

'start:
' Print "Waiting for data..."

Storage$ = ""
MessageLength = 20

SETTICK 500, ProcessMessages
Loopything:
' Print Time$
GoTo loopything


ProcessMessages:
Print "Waiting for data..."
A$=Retrieve$()
IF LEN(A$) > 0 then Process(A$)
IRETURN


SerialInt:
DO
a$ = INPUT$(25, #5)
'user function Store to be written, only add to 'Store' when a$ contains data
' print a$
if a$ <> "" then
b = Stores(a$)
End If
LOOP UNTIL a$ =""
IReturn


Sub Process(message$)
print "MESSAGE: " message$
ENd Sub


FUNCTION Retrieve$()
LOCAL Message$
LOCAL SeparatorPosition
'retry:
IF (LEN(Storage$) >= MessageLength) THEN
'At least one possible message in storage
'Find the message separator
'SeperatorPosition = INSTR(Storage$,CHR$(13))
SeperatorPosition = INSTR(Storage$,"$")

' IF (SeperatorPosition <> MessageLength) THEN
'Corrupt message (too short or too long) at the beginning of the Storage
'Correct it by removing the corrupt part
' Storage$ = MID$(Storage$, SeperatorPosition + 1)
' GOTO retry
' ENDIF

'Extract the message
Retrieve$ = MID$(Storage$, 1, MessageLength)
'Remove from storage
Storage$ = MID$(Storage$, MessageLength+1)

ELSE
'Storage contains less then MessageLength characters. No complete message available
Retrieve$ = ""
ENDIF
END FUNCTION



Function Stores(message$)
LOCAL MsgLength
' MsgLength = -1;
MsgLength = LEN(message$)
IF (LEN(Storage$) + MsgLength > 255) THEN
'The error will stop program execution. Good while testing
print Storage$
ERROR "Not enough storage available!"
'In normal mode set MsgLength to -1.
'This will inform the caller that the message is not stored.
MsgLength = -1;
ELSE
Storage$ = Storage$ + message$
ENDIF
Stores = MsgLength
END FUNCTION

MESSAGE: ä ÿ ÿ kÿÿÿç~
Waiting for data...
MESSAGE: 
€ -LD ä ÿ
Waiting for data...
MESSAGE: ÿ 'ÿÿç~
€ -LD
Waiting for data...
MESSAGE: ä ÿ ÿ 'ÿÿç~
Waiting for data...
MESSAGE:
€ -LD ä ÿ ÿ
Waiting for data...
MESSAGE: 'ÿÿÿç~
€ -LD
Waiting for data...
MESSAGE: ä ÿ ÿ 'ÿÿÿÿç~
Waiting for data...
MESSAGE: 9
€ -LD ä ÿ
Waiting for data...
MESSAGE: ÿ ÿÿç~
€ -LD
Waiting for data...
MESSAGE: ä ÿ ÿ 'ÿÿÿç~

231
126
0
13
0
127

For (i=0, checksum=0; i<cnt; i++)
checksum = checksum ^ data; 'XOR all the bytes

checksum = ~checksum 'invert value

A$ = "A"

if A$ = chr$(65) ....
if A$ = chr$(&H41) ....
if A$ = chr$(&O101) ....

The easiest will be:
if A$ = "A"

A = ASC(A$)
if A = 65 ......
if A = &H41 .....
if A = &O101

the most meaningful might be
if A = ASC("A")

Dim STRING S1Buffer(512) LENGTH 1, S1Message LENGTH 75, S1MsgPast LENGTH 1
DIM S1Capacity=512, S1Counter=0, S1Head=0, S1Tail=0, S1MsgFlag=0, S1MsgLen=0

OPEN "COM1: 57600, 256, S1_WriteBuf, 1, INV" AS #1
OPEN "COM2: 9600, 256, Serial2_Int, 1" AS #2

SETTICK 2, S1_ReadBuf, 1

Print "Program Started:" TIME$
Print #2, "Program Started:" TIME$

Loopything:
GoTo loopything


S1_WriteBuf:
Local string msg LENGTH 1

msg = INPUT$(1, #1)
IF S1Counter = S1Capacity then
S1Counter = 0
ERROR "Serial 1 Buffer FULL"
End If

S1Buffer(S1Tail) = msg
S1Tail = S1Tail + 1
IF S1Tail > S1Capacity then S1Tail = 0
S1Counter = S1Counter + 1

IReturn



S1_ReadBuf:
local string msg LENGTH 1

If S1Counter > 0 then
msg = S1Buffer(S1Head)
S1Head = S1Head + 1
IF S1Head > S1Capacity THEN S1Head = 0
S1Counter = S1Counter - 1

If S1MsgPast = CHR$(231) AND msg = CHR$(126) THen 'Start of a new message (Header1 0xE7 Header2 0x7E)
S1MsgFlag = 1
S1Message = CHR$(231)
End If
If Len(S1Message) > 74 Then S1Message = "" 'If data is longer then 74, something went wrong and reset
If S1MsgFlag = 1 Then S1Message = S1Message + msg 'Append byte from Buffer to Message string

If Len(S1Message) = 8 Then S1MsgLen = ASC(msg) 'Payload length section

If Len(S1Message) = S1MsgLen+9 Then 'Read the whole message, payload + header

S1_Process(S1Message)
S1MsgFlag = 0
S1Message = ""
ENd If
S1MsgPast = msg

End If

IRETURN



SUB S1_Process(msg as String LENGTH 75)

Local STRING MajorId LENGTH 1, MinorId LENGTH 1, CommandNum LENGTH 1, Source LENGTH 1, Destination LENGTH 1, PayloadData LENGTH 74, CheckSum LENGTH 1
Local x=0, PayloadLength=0, CheckSumCal=0

MajorId = MID$(msg,3,1)
MinorId = MID$(msg,4,1)
CommandNum = MID$(msg,5,1)
Source = MID$(msg,6,1)
Destination = MID$(msg,7,1)
PayloadLength = ASC(MID$(msg,8,1))
PayloadData = MID$(msg,9,PayloadLength)
CheckSum = RIGHT$(msg,1) 'last byte
x = 1
DO
CheckSumCal = CheckSumCal XOR ASC(MID$(msg, x, 1))
x = x + 1
LOOP UNTIL x = Len(msg)
CheckSumCal = CheckSumCal XOR 255 'Invert the summed value

If ASC(CheckSum) <> CheckSumCal Then
PRINT "Error: Corrupt message " CheckSum " = " HEX$(CheckSumCal)
Exit Sub
End If


PRint #2, "VPX_Status:" msg 'SEND to Tablet


End If

ENd Sub

'****************************** SERIAL 1 ***************************
S1_WriteBuf:

Local string msg LENGTH 1
DO
msg = INPUT$(1, #1)

If S1MsgPast = CHR$(VPX_Header1) AND msg = CHR$(VPX_Header2) THen 'Start of a new message (Header1 0xE7 Header2 0x7E)
S1MsgFlag = 1
S1Message = CHR$(VPX_Header1)
End If

If Len(S1Message) = 3 AND S1MsgPast = CHR$(&h12) Then 'Major - Check what contstant rate message we are about to receive
If (msg = CHR$(&h02) OR msg = CHR$(&h03)) THen S1MsgFlag = 0 'Minor - Do not care about flap & fault
End If

If S1MsgFlag = 1 Then
S1Message = S1Message + msg 'Append byte from Buffer to Message string

If Len(S1Message) = 8 Then S1MsgLen = ASC(msg) 'Payload length section

If Len(S1Message) = S1MsgLen+9 Then 'Read the whole message, header + payload

If INSTR(S1Message,CHR$(&h12) + CHR$(&h00)) > 0 Then VPX_SystemStatus = S1Message
If INSTR(S1Message,CHR$(&h12) + CHR$(&h01)) > 0 Then VPX_DeviceStatus = S1Message

S1MsgFlag = 0
ENd If
ENd If

S1MsgPast = msg
LOOP UNTIL msg=""

IReturn