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The ZMODEM routines in zm.c accept an option to escape all control |
characters, to allow operation with less transparent networks. This |
option can be given to either the sending or receiving program. |
7.3 HHHHeeeeaaaaddddeeeerrrr |
All ZMODEM frames begin with a header which may be sent in binary or HEX |
form. ZMODEM uses a single routine to recognize binary and hex headers. |
Either form of the header contains the same raw information: |
o+ A type byte[2] [3] |
o+ Four bytes of data indicating flags and/or numeric quantities depending |
on the frame type |
__________ |
2. The frame types are cardinal numbers beginning with 0 to minimize |
state transition table memory requirements. |
3. Future extensions to ZMODEM may use the high order bits of the type |
byte to indicate thread selection. |
Chapter 7 Rev 10-27-87 Typeset 10-27-87 13 |
Chapter 7 ZMODEM Protocol 14 |
FFFFiiiigggguuuurrrreeee 1111.... Order of Bytes in Header |
TYPE: frame type |
F0: Flags least significant byte |
P0: file Position least significant |
P3: file Position most significant |
TYPE F3 F2 F1 F0 |
------------------- |
TYPE P0 P1 P2 P3 |
7.3.1 11116666 BBBBiiiitttt CCCCRRRRCCCC BBBBiiiinnnnaaaarrrryyyy HHHHeeeeaaaaddddeeeerrrr |
A binary header is sent by the sending program to the receiving program. |
ZDLE encoding accommodates XON/XOFF flow control. |
A binary header begins with the sequence ZPAD, ZDLE, ZBIN. |
The frame type byte is ZDLE encoded. |
The four position/flags bytes are ZDLE encoded. |
A two byte CRC of the frame type and position/flag bytes is ZDLE encoded. |
0 or more binary data subpackets with 16 bit CRC will follow depending on |
the frame type. |
The function _z_s_b_h_d_r transmits a binary header. The function _z_g_e_t_h_d_r |
receives a binary or hex header. |
FFFFiiiigggguuuurrrreeee 2222.... 16 Bit CRC Binary Header |
* ZDLE A TYPE F3/P0 F2/P1 F1/P2 F0/P3 CRC-1 CRC-2 |
7.3.2 33332222 BBBBiiiitttt CCCCRRRRCCCC BBBBiiiinnnnaaaarrrryyyy HHHHeeeeaaaaddddeeeerrrr |
A "32 bit CRC" Binary header is similar to a Binary Header, except the |
ZZZZBBBBIIIINNNN (A) character is replaced by a ZZZZBBBBIIIINNNN33332222 (C) character, and four |
characters of CRC are sent. 0 or more binary data subpackets with 32 bit |
CRC will follow depending on the frame type. |
The common variable _T_x_f_c_s_3_2 may be set TRUE for 32 bit CRC iff the |
receiver indicates the capability with the CCCCAAAANNNNFFFFCCCC33332222 bit. The zgethdr, |
zsdata and zrdata functions automatically adjust to the type of Frame |
Check Sequence being used. |
FFFFiiiigggguuuurrrreeee 3333.... 32 Bit CRC Binary Header |
* ZDLE C TYPE F3/P0 F2/P1 F1/P2 F0/P3 CRC-1 CRC-2 CRC-3 CRC-4 |
7.3.3 HHHHEEEEXXXX HHHHeeeeaaaaddddeeeerrrr |
The receiver sends responses in hex headers. The sender also uses hex |
headers when they are not followed by binary data subpackets. |
Chapter 7 Rev 10-27-87 Typeset 10-27-87 14 |
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