6.0 COMMUNICATIONS PROTOCOL
GENERAL DEFINITIONS:
[STX] - 02h - Start of data [ETX] - 03h - End of data [ACK] - 06h - Acknowledge [NAK] - 15h - Negative Acknowledge [DLE] - 10h - Data Link Escape [CMD]
[CSM] - xxh - Checksum, 2’s complement sum of the data between the [STX] and [ETX] characters
GENERAL NOTES:
1.The use of brackets in this document means that there is a single byte of information contained within the brackets. This convention is used to insure that the construction of the message is clear.
2.If the below message was sent, the following checksum would be computed:
DLE STX UID CMD | DATA | DLE ETX CSM |
[10][02] [01] [82] [00][00][10][10][00] [10] [03] [6D]
Note the delimited datum character. Since a 10h is the DLE, the only way the software can know that a 10h in the middle of a data word is datum and not the DLE is to put the datum in twice. The driver software must know that a single 10h is the DLE and not datum! The driver software must actually use only one 10h to compute the check- sum value.
01 + 82 + 00 + 00 + 10 + 00 = 93: 2’s complement = 6D
3.All data is sent in four bytes regardless of the needed length of data. For instance, parameter 48 has the value of 0 for jump and 1 for MOP. The actual parameter is passed in communications however as a [00][00][00][00] for jump mode and a [00][00][00][01] for MOP mode. In this way, all data has an expected length of 4 bytes.
Revised 7/95 | Page 45 | |
POWERTEC Ind. Corp.© |
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