48
Command Summary
Table 45: XModem File Upload Protocol
Host
Display
Comments
254
Command Prefix
220
XModem Upload Command
133
Command Byte One
6
Command Byte Two
48
Command Byte Three
1
File ID LSB
0
File ID MSB
1
File Type
0
Size LSB
0
Size
1
Size
0
Size MSB
67
C (If file fits)
1
Start of Header
128
Block Count
127
Inverted Block Count (255-Count)
<128 B>
128 Byte Data Block
30
*
CRC MSB
71
*
CRC LSB
6
ACK (NAK if counts don’t match)
…
…
…
4
End of Transmission
6
ACK (NAK if EOT is not expected)
Table 46: XModem File Download Protocol
Host Display
Comments
254
Command Prefix
221
XModem Download Command
133
Command Byte One
6
Command Byte Two
48
Command Byte Three
1
File ID LSB
0
File ID MSB
1
File Type
0
Size LSB (NAK if not found)
0
Size
1
Size
0
Size MSB
67
C
1
Start of Header
128
Block Count
127
Inverted Block Count (255-Count)
<128 B>
128 Byte Data Block
30
*
CRC MSB
71
*
CRC LSB
6
ACK (NAK if counts don’t match)
…
…
…
4
End of Transmission
6
ACK (NAK if EOT is not expected)
Table 47: XModem Message Bytes
Value
Action
Description
1
Start of Header
Begin upload transfer
4
End of Transmission
End completed upload transfer
6
Acknowledged
Transfer successful, upload continues
21
Not Acknowledged
Transfer failed, upload aborted
67
C
Confirmation that file will fit
*Note:
CRC bytes are calculated using the XMODEM CRC-CCITT algorithm available at:
http://www.matrixorbital.ca/appnotes/XModem/ymodem.txt
.
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