Carrol Touch TouchSystems CarrollTouch Prog, Programmer'S Manual, Page: 69 / 274

Chapter 5 - Smart-Frame Protocol II CARROLL TOUCH
5-12 Touch System Programmer’s Guide
Error Reporting
SFP-II uses a command error status parameter (Cmderr) to report errors
in commands sent to the touch system. The one-byte parameter is part
of every SFP-II report and indicates whether the SFP-II command
number and/or command parameters were valid.
Note
The use of the Cmderr parameter to indicate unsupported features
is especially useful during the period that the SFP-II specification
is being developed. Features that have been specified but not yet
implemented will be indicated in this manner. The host should
check Cmderr in all reports returned from the touch system to
recognize these unsupported features.
Cmderr has a value of 0 if the command number and parameters are all
valid, or if the report is an unsolicited report.
When an error occurs, the command number and parameter bytes (if
any) that were sent by the host are echoed to the host in the
corresponding report. The touch system does not take any of the actions
and/or change the values of any of the parameters in the command.
Invalid Command Number
When an invalid command number is detected, an SFP-II report packet
is sent with Cmderr set to
FF
.
For example, if function 93H is undefined and the host sends the
following command:
66 01 93 FF
The touch system responds with the following report:
E0 02 FF 93 FF
The first
FF
byte is Cmderr and indicates that there is no command
defined with an opcode value of 93H.
If function 94H is undefined and the host sends the following
command:
66 04 94 01 02 03 FF