Carrol Touch TouchSystems CarrollTouch Prog, Руководство программиста

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Chapter 5 - Smart-Frame Protocol II CARROLL TOUCH
5-6 Touch System Programmer’s Guide
respond after another timeout period, the host should send enough FFH
bytes to ensure that the touch system’s input buffer overflows, and then
retry the command again. Note that the host could certainly send the
FFH bytes without retrying the command if it so chose. Refer to “Error
Reporting,” later in this chapter, for more details on error handling.
This design greatly simplifies the handling of command and report
packets for the touch system and the host. The touch system cannot
queue up command packets from the host, thus preventing many
potential overrun and timing problems.
Commands
An SFP-II command has the format:
header packetbytecount commandnumber
optionalparameters trailer
header
= Defined to be 66H.
packetbytecount
= Length of the command the command
parameters (if any) in bytes. For example, a command
with two bytes of parameters has a byte count of 3 (one
byte for the command number and two bytes for the
parameters).
commandnumber
= One byte opcode that identifies the SFP-II command.
Valid opcodes are 00H through BFH.
optionalparameters
= Parameters for the SFP-II command. The maximum
number of parameter bytes is 252 (FCH).
trailer
= Defined to be FFH.
The maximum length of an SFP-II command packet is 256 bytes.
The format for SFP-II commands reflects the fact that SFP-II is a
layered protocol. There are two layers, the validation layer and the
interpretation layer.