Technical pages
XMODEM protocol
Instructions
Use
Example
Principe
The XMODEM protocol allows to make files transfers by blocks
of 128 bytes with error detection and correction by rehearsal.
Here is an example of data transfer under protocol XMODEM
protocol with:
<soh> = 0x01
<nak> = 0x15
<ack> = 0x06
<eot> = 0x04
<data> = 128 bytes of data
<xx > = checksum of the line (from <soh> to <data>
include)
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Transmiter
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Receiver
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Wait of 10 seconds at most
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<<<
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<nak>
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<soh> 0x01 0xFE <data> <xx>
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>>>
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<<<
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<ack>
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<soh> 0x02 0xFD <data> <xx>
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>>>
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Error of transmission
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<<<
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<nak>
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<soh> 0x02 0xFD <data> <xx>
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>>>
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Rehearsal successfully
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<<<
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<ack>
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<soh> 0x03 0xFC <data> <xx>
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>>>
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<<<
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<ack>
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<eot>
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>>>
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<<<
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<ack>
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Instructions
- XMODEM_TAMPON address
128 bytes transmission/reception buffer adress
- XMODEM_BLOC address
Variable containing the number of block in
the course of transfer
- XMODEM_TEMPO address
Variable for temporizations management bound
to the protocol
- INPUT_FILE? nbr_bytes
Instruction giving the number of available
bytes in INPUT_FILE
- RS232_RECEIVE_FILE? nbr_bytes
Instruction giving the number of available
bytes in RS232_RECEIVE_FILE
- RS232_TRANSMIT_FILE? nbr_bytes
Instruction giving the number of available
bytes in RS232_TRANSMIT_FILE
- OUTPUT_FILE? nbr_bytes
Instruction giving the number of available
bytes in OUTPUT_FILE
- T_XMODEM_CONNECTE address
XMODEM management task (replace T_RS232_CONNECTE
during the duration of the transfer)
rec/emi XMODEM_OUVRE error
Opening of a XMODEM transfer in transmission
if rec/emi is zero or in reception otherwise.
error is zero when operation is correct
- XMODEM_OCTET_RECOIT byte,error
Reception of a byte.
error is zero if the byte is valid, otherwise
reception is ended
byte XMODEM_OCTET_EMET error
Transmission of a byte.
error is zero if the transmission is correct
- XMODEM_FERME -
At the end of the transfer in transmission
or in reception
address XMODEM_RECOIT length
Reception of a file at address specified
on the length (in bytes) indicated at the end of transfer
address,length XMODEM_EMET -
Transmission of a file situated at address
and on the length (in bytes) specified
Use
The transfer of a file requires the
use of the following instructions:
- XMODEM_OUVRE,
- XMODEM_OCTET_RECOIT or XMODEM_OCTET_EMET,
- XMODEM_FERME.
The user has to start a transfer by the instruction "XMODEM_OUVRE"
with a value zero in the case of a transmission, and not zero
in the case of a reception. A zero error code indicates that the
transfer can be made correctly.
Instruction "XMODEM_FERME" must be necessarily
executed in the end of a file transmission operation. The las
block will be completed automatically with stuffing bytes (in
0), transferred and followed by the transmission of the end of
text character ( eot ).
Files can be transferred by using "Hyperterminal"
software on PC or " Apple works terminal" on MAC.
Example
To illustrate this page, here is the
code of instructions "XMODEM_RECOIT" and "XMODEM_EMET":
: XMODEM_RECOIT ( address --> length )
-1 XMODEM_OUVRE
IF
DROP 0
ELSE
0
BEGIN
XMODEM_OCTET_RECOIT
IF
DROP -1
ELSE
3 PICK C! >R 1+ R> 1+ 0
THEN
UNTIL
SWAP DROP
THEN
XMODEM_FERME
;
: XMODEM_EMET ( address, length --> - )
0 XMODEM_OUVRE
IF
DROP
ELSE
0 DO
DUP C@ XMODEM_OCTET_EMET
IF
LEAVE
THEN
1+
LOOP
THEN
DROP XMODEM_FERME
;
