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YMODEM refers to the XMODEM/CRC protocol with batch transmission and
optional 1024 byte blocks as described in YMODEM.DOC.[1]
6. ZZZZMMMMOOOODDDDEEEEMMMM RRRREEEEQQQQUUUUIIIIRRRREEEEMMMMEEEENNNNTTTTSSSS
ZMODEM requires an 8 bit transfer medium.[1] ZMODEM escapes network
control characters to allow operation with packet switched networks. In
general, ZMODEM operates over any path that supports XMODEM, and over many
that don't.
To support full streaming,[2] the transmission path should either assert
flow control or pass full speed transmission without loss of data.
Otherwise the ZMODEM sender must manage the window size.
6.1 FFFFiiiilllleeee CCCCoooonnnntttteeeennnnttttssss
6.1.1 BBBBiiiinnnnaaaarrrryyyy FFFFiiiilllleeeessss
ZMODEM places no constraints on the information content of binary files,
except that the number of bits in the file must be a multiple of 8.
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1. Available on TeleGodzilla as part of YZMODEM.ZOO
1. The ZMODEM design allows encoded packets for less transparent media.
2. With XOFF and XON, or out of band flow control such as X.25 or CTS
Chapter 6 Rev 10-27-87 Typeset 10-27-87 10
Chapter 6 ZMODEM Protocol 11
6.1.2 TTTTeeeexxxxtttt FFFFiiiilllleeeessss
Since ZMODEM is used to transfer files between different types of computer
systems, text files must meet minimum requirements if they are to be
readable on a wide variety of systems and environments.
Text lines consist of printing ASCII characters, spaces, tabs, and
backspaces.
6.1.2.1 AAAASSSSCCCCIIIIIIII EEEEnnnndddd ooooffff LLLLiiiinnnneeee
The ASCII code definition allows text lines terminated by a CR/LF (015,
012) sequence, or by a NL (012) character. Lines logically terminated by
a lone CR (013) are not ASCII text.
A CR (013) without a linefeed implies overprinting, and is not acceptable
as a logical line separator. Overprinted lines should print all important
characters in the last pass to allow CRT displays to display meaningful
text. Overstruck characters may be generated by backspacing or by
overprinting the line with CR (015) not followed by LF.
Overstruck characters generated with backspaces should be sent with the
most important character last to accommodate CRT displays that cannot
overstrike. The sending program may use the ZZZZCCCCNNNNLLLL bit to force the
receiving program to convert the received end of line to its local end of
line convention.[3]
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3. Files that have been translated in such a way as to modify their
length cannot be updated with the ZZZZCCCCRRRREEEECCCCOOOOVVVV Conversion Option.