Synchronet v3.21e-Win32 (install) has been released (Mar-2026).

You can donate to the Synchronet project using PayPal.

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revisionPrevious revision
Next revision		Previous revision
ref:zmodem [2018/03/01 12:11] – Links to util:binkit changed to module:binkit digital manref:zmodem [2025/09/26 14:13] (current) – [ZMODEM Frame] Mention the Tera Term 0x8D 0x8A oddity digital man
Line 63: Line 63:
  
 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. A carriage-return (CR) character may precede the linefeed (LF) character.
 +
 +Some ZMODEM implementations send this terminating LF with the high bit set (0x8A, that's ASCII-LF with an even-parity bit set). Some ZMODEM implementations (e.g. Tera Term) inexplicably send **both** CR and LF characters with the parity bit set (i.e. 0x8D 0x8A).
 +
 +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 =====
Line 601: Line 685:
 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
Line 858: Line 942:
  
 ===== See Also ===== ===== See Also =====
-  * [[module:binkit]] +  * [[util:sexyz]]
-  * [[http://omen.com/]] +
   * [[:ref:|Reference Library]]   * [[:ref:|Reference Library]]
  
 {{tag>zmodem}} {{tag>zmodem}}
  

Trace: • ZMODEM