• Xmodem Hyperterminal Download
• Cisco Xmodem

Nice and simple, this helped me a lot when writing an interface to a 'Flashrunner' box that loads files using ymodem, in my case through Ethernet. However I found a couple of problems that might help others:.According to, the receiver sends a 'C' character immediately after the ACK of block 0 to request transmission of a 16-bit (as opposed to 8-bit) CRC.

My box did exactly that. The above code will read that response after transmission of block 1, displaying a '?'

Status, and all subsequent responses will be interpreted 1 block late. As a result if the receiver requests retransmission using a NAK response the wrong block will be retransmitted.At the end of the file a second EOT should not be sent unconditionally for ymodem.

The specification says: 'At the end of each file, the sending program shall send EOT up to ten times until it receives an ACK character. (This is part of the XMODEM spec.)'. In my case I get an ACK after the first EOT.

The spec also says that a 'C' follows the ACK of the EOT, which was true in my case.Ymodem is a batch file transfer. After the EOT(s) the receiver waits for another file. In my case I needed to tell it that the batch had finished by sending a null block 0 ( payload all zero, crc = 0) as described in the specification so that it didn't hang and could carry on and do other things. This is acknowledged with an ACK and a 'C' as for any other block 0.

This is the reason I had to write my own code instead of just using the Linux sb command; I couldn't work out a way to get sb to do that. Nice and simple, this helped me a lot when writing an interface to a 'Flashrunner' box that loads files using ymodem, in my case through Ethernet. However I found a couple of problems that might help others:.

According to, the receiver sends a 'C' character immediately after the ACK of block 0 to request transmission of a 16-bit (as opposed to 8-bit) CRC. My box did exactly that. The above code will read that response after transmission of block 1, displaying a '?'

Status, and all subsequent responses will be interpreted 1 block late. As a result if the receiver requests retransmission using a NAK response the wrong block will be retransmitted. At the end of the file a second EOT should not be sent unconditionally for ymodem. The specification says: 'At the end of each file, the sending program shall send EOT up to ten times until it receives an ACK character. (This is part of the XMODEM spec.)'. In my case I get an ACK after the first EOT.

The spec also says that a 'C' follows the ACK of the EOT, which was true in my case. Ymodem is a batch file transfer. After the EOT(s) the receiver waits for another file. In my case I needed to tell it that the batch had finished by sending a null block 0 ( payload all zero, crc = 0) as described in the specification so that it didn't hang and could carry on and do other things.

This is acknowledged with an ACK and a 'C' as for any other block 0. This is the reason I had to write my own code instead of just using the Linux sb command; I couldn't work out a way to get sb to do that.+1 for an effort to write down the the missing details. Anyone who'll use this code follow these instructions to get the correct result.According to, the receiver sends a 'C' character immediately after the ACK of block 0 to request transmission of a 16-bit (as opposed to 8-bit) CRC. My box did exactly that.

The above code will read that response after transmission of block 1, displaying a '?' Status, and all subsequent responses will be interpreted 1 block late. As a result if the receiver requests retransmission using a NAK response the wrong block will be retransmitted.At the end of the file a second EOT should not be sent unconditionally for ymodem. The specification says: 'At the end of each file, the sending program shall send EOT up to ten times until it receives an ACK character. (This is part of the XMODEM spec.)'. In my case I get an ACK after the first EOT. The spec also says that a 'C' follows the ACK of the EOT, which was true in my case.Ymodem is a batch file transfer.

After the EOT(s) the receiver waits for another file. In my case I needed to tell it that the batch had finished by sending a null block 0 ( payload all zero, crc = 0) as described in the specification so that it didn't hang and could carry on and do other things. This is acknowledged with an ACK and a 'C' as for any other block 0. This is the reason I had to write my own code instead of just using the Linux sb command; I couldn't work out a way to get sb to do that.Thanks for this. I don't currently have a setup to test and fix the missing pieces.

Xmodem Hyperterminal Download

Cisco Xmodem

If you want, please send me a patch so I can add that here for reference.