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PPX-1 Protocol

The following is the format of the PPX-1 packet:

BYTE SOH ;Start of header for synchronization

(ASCII 01H)

BYTE LEN H ;High byte of length

BYTE LEN L ;Low byte of length

BYTE HEADER ;= NOT(LEN L) +

CHECK ;NOT(LEN H), this is an

; arithmetic sum

BYTES DATA ;This is where the MCP COMM-

;AND is contained (see section 3)

BYTE CHECK- ;16 bit check sum of data

SUM H

BYTE CHECKSUM L

Note that the LEN field is the length of the DATA section, not

including the CHECKSUM field.

The purpose of the header is to make frame synchronization

easier. In asynchronous communications where the data field may

have any ASCII value, this is a difficult problem. The HEADER

CHECK field is intended to provide a fairly secure way of mak-

ing sure that a header has actually been found.

The maximum permissible packet length is 1456 bytes (not

including the header and checksum).

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Proxim 7910 Guía de usuario Pagina 79