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%
dim float t!,ttx!,tmr!

baud%=1843200 ' 115200 230400 460800 1843200
Open "com1:"+Str$(baud)+",2000000" As #1
fn$="tst.txt"
print "Trying to get "+fn$
open "\"+fn$ for output as #2
print #1,fn$+xon;
oldloc%=0
cksum%=0
nChar%=0
timer=0
do while loc(#1) = 0 and timer < 10000: loop
if loc(#1) = 0 then
 print "File Not Received: "+fn+"--exiting"
 print #1,chr$(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%>1000000 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)"