open "com1:115200" as #1

setpin 3,din    'connected to RTS
setpin 5,dout   'connected to CTS
pin(5)=pin(3)   'set default

i=0
'print characters until RTS becomes high
do
 print #1,"@";  
 i=i+1
loop until inkey$=chr$(27) or pin(3)=1
print i;" characters have been sent"

'open com port with hardware handshaking
Open "/dev/ttyUSB0: 115200, RTSCTS" As #1

'do not read any characters until a keyboard key is pressed
do:loop until inkey$<>""

i=0
'now read all characters in the serial buffers and count the characters
do while LOC(1)>0
a$=input$(1,#1)
i=i+1
loop
print i;" characters read"

   case Key of            // alt key functions...
{$IFDEF WINDOWS}
               ord('1'):if CONNECTED=2 then try EscapeCommFunction(SerialHandle, SETDTR) except end;          // set DTR
               ord('2'):if CONNECTED=2 then try EscapeCommFunction(SerialHandle, CLRDTR) except end;          // clear DTR
               ord('3'):if CONNECTED=2 then try EscapeCommFunction(SerialHandle, SETRTS) except end;          // set RTS
               ord('4'):if CONNECTED=2 then try EscapeCommFunction(SerialHandle, CLRRTS) except end;          // clesr RTS
{$ELSE}
               ord('1'):if CONNECTED=2 then try I:=TIOCM_DTR; FpIOCtl(SerialHandle, TIOCMBIS, @I) except end;         // set DTR
               ord('2'):if CONNECTED=2 then try I:=TIOCM_DTR; FpIOCtl(SerialHandle, TIOCMBIC, @I) except end;         // clear DTR
               ord('3'):if CONNECTED=2 then try I:=TIOCM_RTS; FpIOCtl(SerialHandle, TIOCMBIS, @I) except end;         // set RTS
               ord('4'):if CONNECTED=2 then try I:=TIOCM_RTS; FpIOCtl(SerialHandle, TIOCMBIC, @I) except end;         // clesr RTS
{$ENDIF}

Dim ls%(256) ' 2048 characters or so depending on OPTION BASE.
System "printenv PATH", ls%()
LongString Print ls%()

' ser2pi.bas
xon$=Chr$(17): xoff$=Chr$(19)
D0=16:D1=5:D2=4:D3=0:D4=2:D5=14:D6=12:D7=13:D8=15:D9=3:Rx=3:D10=1:Tx=1
SERIAL2.MODE 115200, D5, D6 ' tx, rx
A$="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
ok$=xoff$
onserial2 received2
k=0

do
 if ok$=xon$ then
   print #2,A$
   k=k+1
   wlog k;" ";
 endif
loop

received2:
 pause 100
 ok$=mid$(serial2.input$,1,1)
return

' sertest.bas
Option explicit
Dim string xon=Chr$(17),xoff=Chr$(19),ack=Chr$(6),nak=Chr$(21),a$,b$,c$,d$,fn$
Dim integer i%,j%,k%,l%,m%,n%,cksum%,oldloc%,baud%,nChar%,maxbuf%
dim float t!,ttx!,tmr!

baud%=115200 '1843200 ' 115200 230400 460800 1843200
maxbuf%=2600
'Open "/dev/ttyAMA0:"+Str$(baud)+",10000" As #1
Open "/dev/ttyUSB0:"+Str$(baud)+",10000" As #1
fn$="test.txt"
print "Trying to get "+fn$
open fn$ for output as #2
'a$=fn$+xon
a$=xon
print #1,a$;
oldloc%=0
cksum%=0
nChar%=0
timer=0
do while loc(#1) = 0 and timer < 10000: loop
if loc(#1) = 0 then
print "File Not Received: "+fn+"--exiting"
print #1,chr$(27); ' EOT
pause 1000
end
endif
timer=0
t!=0
ttx!=0
tmr!=timer
do
l%=loc(#1)
if l%=0 then ' transmission done
  if cksum%>0 then ' something received
    print #1,str$(nChar%)+","+str$(cksum%)+xoff
    print " Bytes, checksum: "+str$(nChar%)+","+str$(cksum%)+xoff
    exit do
  else
    pause 2000 ' allow more time for start-up
    if loc(#1) = 0 then ' nothing received
      print "File Not Received--exiting"
'        exit do
      print #1,xon;
    endif
  endif
elseif l%>maxbuf% or oldloc%=l% then ' this block is done; xoff and write to SD card
  print #1,xoff;
  ttx!=ttx!+(timer-tmr!):
  print "*";
  do while loc(#1) > 0 ' clear all characters from buffer
    b$=input$(255,#1)
    j%=Len(b$)
    For i%=1 To j%
      c$=Mid$(b$,i%,1)
      cksum%=cksum%+Asc(c$)
      nChar%=nChar%+1
    Next i%
    print #2,b$;
  loop
  print #1,xon;
  tmr!=timer
endif
oldloc%=l%
pause 1000 ' wait a second
loop
t!=timer
print #1,chr$(27); ' EOT
on error skip 1
close #1
on error skip 1
close #2
print nChar%;" Characters; ";t!/1000;" seconds; ";ttx!/1000;" seconds transmitting; checksum: ";cksum%
print int(nChar%/(t!/1000));" bytes per second total; ";int(nChar%/(ttx!/1000));" bytes per second (to transmit)"

> run
Trying to get test.txt
*********************** Bytes, checksum: 65411,4770529
65411 Characters;  64.122 seconds;  51.025 seconds transmitting; checksum:  4770529
1020 bytes per second total;  1281 bytes per second (to transmit)
>

' ser2pi.bas
Dim integer k
xon$=Chr$(17): xoff$=Chr$(19)
A$="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
ok$=xoff$
SetPin 21,uart0tx:SetPin 22,uart0rx ' : Open "com0:9600" As #1
Open "COM0:115200" As #2
k=0

Do
 If ok$=xon$ Then
   Print #2,A$
   k=k+1
   Print k;" ";
   Pause 3
 EndIf
 If Loc(2) > 0 Then
   b$=Input$(1,# 2)
   If b$=xon$ Or b$=xoff$ Then: ok$=b$: EndIf
 EndIf
Loop

' sertest.bas
Option explicit
Dim string xon=Chr$(17),xoff=Chr$(19),ack=Chr$(6),nak=Chr$(21),a$,b$,c$,d$,fn$
Dim integer i%,j%,k%,l%,m%,n%,cksum%,oldloc%,baud%,nChar%,maxbuf%
dim float t!,ttx!,tmr!

baud%=115200 '1843200 ' 115200 230400 460800 1843200
maxbuf%=2600
'Open "/dev/ttyAMA0:"+Str$(baud)+",10000" As #1
Open "/dev/ttyUSB0:"+Str$(baud)+",10000" As #1
fn$="test.txt"
print "Trying to get "+fn$
open fn$ for output as #2
'a$=fn$+xon
a$=xon
print #1,a$;
oldloc%=0
cksum%=0
nChar%=0
timer=0
do while loc(#1) = 0 and timer < 10000: loop
if loc(#1) = 0 then
print "File Not Received: "+fn+"--exiting"
print #1,chr$(27); ' EOT
pause 1000
end
endif
timer=0
t!=0
ttx!=0
tmr!=timer
do
l%=loc(#1)
if l%=0 then ' transmission done
  if cksum%>0 then ' something received
    print #1,str$(nChar%)+","+str$(cksum%)+xoff
    print " Bytes, checksum: "+str$(nChar%)+","+str$(cksum%)+xoff
    exit do
  else
    pause 2000 ' allow more time for start-up
    if loc(#1) = 0 then ' nothing received
      print "File Not Received--exiting"
'        exit do
      print #1,xon;
    endif
  endif
elseif l%>maxbuf% or oldloc%=l% then ' this block is done; xoff and write to SD card
  print #1,xoff;
  ttx!=ttx!+(timer-tmr!):
  print "*";
  do while loc(#1) > 0 ' clear all characters from buffer
    b$=input$(255,#1)
    j%=Len(b$)
    For i%=1 To j%
      c$=Mid$(b$,i%,1)
      cksum%=cksum%+Asc(c$)
      nChar%=nChar%+1
    Next i%
    print #2,b$;
  loop
  print #1,xon;
  tmr!=timer
endif
oldloc%=l%
pause 1000 ' wait a second
loop
t!=timer
print #1,chr$(27); ' EOT
on error skip 1
close #1
on error skip 1
close #2
print nChar%;" Characters; ";t!/1000;" seconds; ";ttx!/1000;" seconds transmitting; checksum: ";cksum%
print int(nChar%/(t!/1000));" bytes per second total; ";int(nChar%/(ttx!/1000));" bytes per second (to transmit)"
open fn$ for input as #2
i%=0: k%=0
do while not eof(#2)
 line input #2,a$
 inc i
 if a$ <> "ABCDEFGHIJKLMNOPQRSTUVWXYZ" then
   inc k
 endif
loop
print i%;" lines read; ";k%;" errors"
close #2

> run
Trying to get test.txt
****** Bytes, checksum: 48356,3519626
48356 Characters;  15.895 seconds;  6.004 seconds transmitting; checksum:  3519626
3042 bytes per second total;  8053 bytes per second (to transmit)
1727 lines read;  0 errors

> run
Trying to get test.txt
XON sent  17
****** Bytes, checksum: 49336,3590956
49336 Characters;  10.731 seconds;  6.002 seconds transmitting; checksum:  3590956
4597 bytes per second total;  8219 bytes per second (to transmit)
1762 lines read;  0 errors