DAP Technology 1394, Руководство по эксплуатации

Страница: 314 / 458

Serial Bus Protocol (SBP)
314 Copyright © DapTechnology B.V., 2005-2019 - All Rights Reserved., 5/20/2019
The command always starts with an operation code field. The format of the remaining bytes depend on
the value of this operation code. A 'switch' item is used to implement the different commands. The
implementation of the 'INQUIRE' command is shown ('case INQUIRE' item expanded) in more detail. One
of its field is the 'cmddt' field. This field is selected and thus the properties of it are dispayed below the
definitions tree. There you can see that it is a one bit field. Notice also that the 'output parameter'
checkbox has been checked, meaning that the formatting of this command packet will result in an output
parameter called 'cmddt' with the value of that bit. We will explain below why this is needed.
In the right pane ('Result' pane), the result of the selected definition ('command') is shown. We see the
'operation code' field at the start. For the 'operation code' field we filled in the value 18 to test the
'INQUIRE' command. It is followed by a reserved field (only visible in the layout view), followed by the one
bit 'cmddt' field, etc. As you can see for this command tree output parameters are generated:
'operation_code', 'cmddt' and 'epvd'. These parameters are used to be able to format the data associated
with the command (see below).
17.2.1.2. Data
The format definition 'data' defines the format of the data block associated with a particular command.
The format of the data depends on the value of the operation code of the command and depending on the
command type, it may depend on other fields from the command. Below the 'data' is shown in more
detail.