Difference between revisions of "Protocols"
| Line 6: | Line 6: | ||
== XModem protocol == | == XModem protocol == | ||
The XModem protocol transmits data in a sequence of blocks. | The XModem protocol transmits data in a sequence of blocks. | ||
=== Basic XModem === | |||
Each block contains 128 bytes of the file to be transmitted. | |||
{| class="xmodem" | {| class="xmodem" | ||
| Line 16: | Line 20: | ||
|} | |} | ||
Each block is defined in this way (numbers tell the number of bytes for each field): | |||
{| class="xmodem" | {| class="xmodem" | ||
| Line 26: | Line 30: | ||
|- | |- | ||
| SOH | | SOH | ||
| Number | |||
| /Number | |||
| Data bytes | |||
| Checksum | |||
|} | |||
The number is a sequence number which increases by one for each successive block. The /Number field is the one's complement of the Number field and calculates as 255-Number. | |||
The checksum field contains the least significant byte of the sum of the data bytes of this block. | |||
The receiver has a timeout of 10 seconds, after which it transmits a NAK. | |||
=== XModem-1K === | |||
XModem-1K is a variation of XModem with 1K (1024) bytes for each data block. | |||
{| class="xmodem" | |||
! 1 | |||
! 1 | |||
! 1 | |||
! style="width:400px" | 1024 | |||
! 1 | |||
|- | |||
| STX | |||
| Number | | Number | ||
| /Number | | /Number | ||
Revision as of 21:01, 7 May 2011
Communication with devices
Here is a commented log when formatting a SSSD floppy disk with the TI disk controller. Actually, this dump was achieved using MESS and putting in some printf lines.
XModem protocol
The XModem protocol transmits data in a sequence of blocks.
Basic XModem
Each block contains 128 bytes of the file to be transmitted.
| Block | Block | Block | ... | Block |
Each block is defined in this way (numbers tell the number of bytes for each field):
| 1 | 1 | 1 | 128 | 1 |
|---|---|---|---|---|
| SOH | Number | /Number | Data bytes | Checksum |
The number is a sequence number which increases by one for each successive block. The /Number field is the one's complement of the Number field and calculates as 255-Number.
The checksum field contains the least significant byte of the sum of the data bytes of this block.
The receiver has a timeout of 10 seconds, after which it transmits a NAK.
XModem-1K
XModem-1K is a variation of XModem with 1K (1024) bytes for each data block.
| 1 | 1 | 1 | 1024 | 1 |
|---|---|---|---|---|
| STX | Number | /Number | Data bytes | Checksum |