Specifications

Chapter 5 - Smart-Frame Protocol II CARROLL TOUCH
5-14 Touch System Programmer’s Guide
66 04 20 01 02 02 FF
If the particular firmware implementation in the touch system does not
support the MultiTouchState value of the TouchStateReportType
parameter (the first 02H byte in the command), the touch system
responds with the following report:
E0 05 02 20 01 02 02 FF
The 02 byte is Cmderr and indicates that the second parameter is in
error. This parameter is the TouchStateReportType parameter. The
value of 02H is a valid value for this parameter and represents a request
by the host that the touch data be returned using the Multi Touch State
Report. However, since this particular firmware does not support the
MultiTouchState reporting method, the touch system returns the error
in Cmderr to indicate this to the host.
Invalid Byte Count
The touch system reports an invalid byte count if it reads the number of
bytes specified by the byte count and the next byte received is not a
command packet trailer byte.
Note that this means that if the number of bytes received after the byte
count is less than the byte count, no error is generated until enough
additional bytes are received to match the byte count or the touch
system’s input buffer overflows. The touch system does not use any
sort of timeout technique if it receives fewer bytes than expected.
This error also occurs if the touch system’s input buffer overflows
while it is attempting to read the number of bytes specified by the byte
count.
When an invalid byte count is detected, an SFP-II report packet is sent
with the Cmderr parameter set to FEH and the SFP-II report number set
to the command number.
For example, suppose the host sends the following command:
66 04 20 01 04 03 FF
Due to noise on the serial line, the touch system actually receives an
extra byte after the first parameter as follows:
66 04 20 01 86 04 03 FF