Synchronet v3.19b-Win32 (install) has been released (Jan-2022).

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ref:zmodem [2020/11/28 15:11] – [See Also] Remove link to omen.com (no longer Chuck's site). :-( digital manref:zmodem [2021/06/29 15:34] (current) – [ZFILE FRAME FILE INFORMATION SUBPACKET] footnote about path/file names with spaces (they are in fact supported in most ZMODEM implemenations) digital man
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 zmodem places no constraints on the content files. zmodem places no constraints on the content files.
 +
 +===== FRAMING =====
 +
 +==== ZMODEM Frame ====
 +There are 2 classes of ZMODEM Frames:
 +  - Hexadecimal (HEX) frames, containing only US-ASCII characters
 +  - Binary (BIN16 or BIN32) frames, containing //almost// all possible octet values
 +
 +=== HEX Frame ===
 +  <frame header> [CR] LF [XON]
 +
 +HEX frames are terminated with an ASCII linefeed character. Some ZMODEM implementations send the HEX frame terminating linefeed character with the high bit set (0x8A, that's ASCII-LF with an even-parity bit set). Also, for some HEX frame types, the frame terminator may be followed by an XON (0x11) character ("transmit on" in so-called "software flow control").
 +
 +=== Binary Frame ===
 +  <frame header> [[<* data subpacket> [...]] <ZCRCW | ZCRCE data subpacket>]
 +  
 +Binary frames may contain zero or more data subpackets (depending on the frame type). The final subpacket of a binary data frame will be of type ZCRCW or ZCRCE.
 +
 +==== Frame Header ====
 +  <frame encoding> <frame type> <frame info> <checksum>
 +
 +**Frame Encoding** (single byte):
 +
 +The //Frame Encoding// is also sometimes called the "Frame Style".
 +
 +^ Style  ^  AKA   ^ Value          ^ Frame Contents                       ^ Checksum   ^
 +| HEX    | ZHEX   | ASCII '''B'''  | Hexadecimal/US-ASCII characters only | 16-bit CRC |
 +| BIN16  | ZBIN   | ASCII '''A'''  | Binary                               | 16-bit CRC |
 +| BIN32  | ZBIN32 | ASCII '''C'''  | Binary                               | 32-bit CRC |
 +
 +Notes:
 +  * All frames sent by the "receiver" must use HEX encoding. 
 +
 +**Frame Type** (single byte):
 +
 +^ Type     ^ Value ^ TX((from sender))^ RX((from receiver)) ^ Info    ^ Data Subpkt    ^ Notes ^
 +| ZRQINIT  | 0x00  |  Y               |  -                  | caps    | -              | Request ZRINIT from the receiver |
 +| ZRINIT   | 0x01  |  -               |  Y                  | caps    | -              | Receiver Initialized |
 +| ZSINIT   | 0x02  |  Y               |  -                  | flags   | Attn sequence  | Sender Initialized |
 +| ZACK     | 0x03  |  Y               |  Y                  | offset  | -              | Positive Acknowledgment |
 +| ZFILE    | 0x04  |  Y               |  -                  | options | File metadata  | File information (name/len/date) |
 +| ZSKIP    | 0x05  |  -               |  Y                  |         | -              | Skip (don't send) this file |
 +| ZNAK     | 0x06  |  Y               |  Y                  |         | -              | Negative Acknowledgment |
 +| ZABORT   | 0x07  |  -               |  Y                  |         | -              | Terminate batch file transfer |
 +| ZFIN     | 0x08  |  Y               |  -                  |         | -              | Terminate transfer session |
 +| ZRPOS    | 0x09  |  -               |  Y                  | offset  | -              | Reposition the send offset |
 +| ZDATA    | 0x0A  |  Y               |  -                  | offset  | File contents  | One or more data subpackets follow |
 +| ZEOF     | 0x0B  |  Y               |  -                  | offset  | -              | End of file reached |
 +| ZFERROR  | 0x0C  |  -               |  Y                  |         | -              | File I/O error |
 +| ZCRC     | 0x0D  |  Y               |  Y                  | CRC-32  | -              | File CRC request/response |
 +| ZFREECNT | 0x11  |  Y               |  -                  | f-space | -              | Request free disk space |
 +
 +**Frame Info**: Up to 15 bytes (but typically 4) of frame type-specific information.\\
 +Note that later claims of //16// bytes of possible frame header data include the //Frame Type// byte.
 +
 +**Frame Header Integrity**: The //Frame Type// and //Frame Info// are integrity-protected with either a 16-bit or 32-bit CRC (determined by the frame encoding).
 +
 +==== Data Subpacket ====
 +  <data> ZDLE <subpacket type> <crc>
 +
 +**ZDLE** is the ZMODEM Data-link-escape character (''^X'', ASCII 24).
 +
 +=== Data Subpacket Length ===
 +
 +  * Data Subpackets may contain up to **1024** bytes of //data// (special octet values are transposed and escaped with //ZDLE//)
 +  * The Data Subpacket Length is also sometimes referred to as the transmit "block size"
 +  * The Data Subpacket Length can be dynamically adjusted by the sender during the transfer of a file, e.g. in response to errors reported by the receiver
 +  * Some ZMODEM implementations (e.g. "ZedZap") support a Data Subpacket Length of up to 8K (8192 bytes)
 +
 +=== Data Subpacket Types ===
 +The Data Subpacket Type is encoded in a single byte.
 +
 +^ Type  ^ ZACK/ZRPOS expected ^ End-of-Frame ^ Meaning    ^ Notes ^
 +| ZCRCW | Yes (synchronous)   | Yes          | Wait or Write | "ZCRCW data subpackets expect a response before the next frame is sent ... to allow the receiver to write its buffer before sending more data"      |
 +| ZCRCE | Only errors         | Yes          | End        | "If the end of file is encountered within a frame, the frame is closed with a ZCRCE data subpacket which does not elicit a response except in case of error"     |
 +| ZCRCQ | Yes (asynchronous)  | No           | Query      | "ZCRCQ subpackets are not used if the receiver does not indicate full duplex ability with the [ZRINIT] CANFDX bit" |
 +| ZCRCG | Only errors         | No           | Go         | "ZCRCG subpackets do not elicit a response unless an error is detected"      |
 +
 +=== Data Subpacket Integrity ===  
 +The Subpacket //data// and //type// bytes are integrity-protected by either a 16-bit or 32-bit CRC.
  
 ===== LINK ESCAPE ENCODING ===== ===== LINK ESCAPE ENCODING =====
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 The pathname (conventionally, the file name) is sent as a The pathname (conventionally, the file name) is sent as a
 null terminated ASCII string.  null terminated ASCII string. 
-No spaces are included in the pathname. +No spaces are included in the pathname. ((some ZMODEM implementations support path/file names that include spaces))
  
 Filename Considerations Filename Considerations

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