Sending an Escape (or binary) character

EazyLink Server, V4.4

During file transfer from the Z88 or the Client an Escape character sequense is sent when a true ESC byte needs to be transmitted, and not a request command. The Escape sequense is as follows:

                      ESC "B" <H1><H2>

where H1 and H2 are the corresponding hexadecimal high and low nibbles of the byte representation.

The actual sequense sent is <ESC "B" "1B"> for the single ESC byte, or

                      27,"B","1","B"

in a simple flow of bytes representing the single ESC byte to be sent. The Escape sequense principle is a copy from the protocol used by the Imp/Export popdown which was used to transfer byte values larger than 127.

The Client or Server need only to use the Escape sequense when transfering binary files (text files like PipeDream files don't contain the ESC character).

The actual PC-LINK II Client application also uses the ESC "B" to transmit 'binary' characters that have ASCII values above 127. This system is redundant, however, PC-LINK II regard it as necessary. All 'binary' ASCII characters, except ESC, are sent normally from the EazyLink Server to the PC-LINK II which receives them perfectly. This scheme seems to be more of a symbolic design than an efficient implementation.