Command Checksums And Crc-8 Checkcodes - Zektor CVS4 User Manual

mal parameter used by the command. For instances if the bits 'AS' and 'IJ' where to be set to 1,
and the rest of the bits set to zero, the parameter value would be calculated as: 8+1, making the
parameter value: 9.
The command to directly set those two bits, and reset all the others would be:
XS 9<CR>
Individual bits of a bitmapped parameter can be set or reset without affecting the other bits, by
prefixing the bitmapped parameter with a '+' to set individual bits, or a '-' to reset individual bits.
For instance in the above example the bitmapped value has been set to '9'. If we would now like
to enable the IR remote, by setting the 'IRE' bit, the following command can be issued:
XS +4<CR>
The will set the 'IR' bit, and have no affect on the others, and the new "XS" value would be: 13
If we'd like to now disable the IR jack and the IR remote functions and the Front Panel, by clear-
ing the 'IRJ', 'IRE' & 'FP' bits, we'd use the value "16+4+2", or 22, and issue the command:
XS -22<CR>
leaving the new "XS" value to be: 1.

Command Checksums and CRC-8 Checkcodes

A checksum or CRC-8 checkcode may be appended to any command, and if given, will be
calculated by the device and compared with the given value. If a mismatch occurs an error will
be returned and the command will not be executed. This can be used to help assure reliable op-
eration in noisy environments. Checksums are more commonly used in serial protocols, however
CRC-8 checkcodes offer a more secure means of insuring error free communications.
A checksum or CRC-8 checkcode is appended to the command by adding a semicolon (';') or
colon (':') suffix character followed by the checksum or checkcode.
An example of appending a checksum to a command:
LI 2,13;178<CR>
the ';' indicates a checksum follows, the '178' is the checksum of the command string up to and
including the ';' character.
In a similar fashion a CRC-8 checkcode can be appended to a command:
LI 2,13:213<CR>
The ':' indicates that a CRC-8 checkcode follows, the '213' is the calculated CRC-8 checkcode.
Optional spaces are allowed before the ';' and ':' characters but NOT after them. The checksum
must immediately follow the ';' character, and a CRC-8 checkcode must immediately follow the ':'
character, anything else, including whitespace, will cause a syntax error to be returned. Similarly
the <CR> must immediately follow the checksum or checkcode parameter or a syntax error will
4 CVS4 Component Video Switch
K.I.S.S.™ (Continued)