Compaq 99875320-5 Manual De Usuario

 
COMMANDS 
 
Most host applications do not need to send commands to the device.  Most host applications only 
need to obtain card data from the device as described previously in this section.  This section of 
the manual can be ignored by anyone who does not need to send commands to the device. 
 
Command requests and responses are sent to and received from the device using feature reports.  
Command requests are sent to the device using the HID class specific request Set_Report.  The 
response to a command is retrieved from the device using the HID class specific request 
Get_Report.  These requests are sent over the default control pipe.  When a command request is 
sent, the device will Nak the Status stage of the Set_Report request until the command is 
completed.  This insures that, as soon as the Set_Report request is completed, the Get_Report 
request can be sent to get the command response.  The usage ID for the command message was 
shown previously in the Usage Table. 

 

The following table shows how the feature report is structured for command requests: 

 

0 Command 

Number 

1 Data 

Length 

2 – 23 

Data 

 

The following table shows how the feature report is structured for command responses. 

 

0 Result 

Code 

1 Data 

Length 

2 – 23 

Data 

 
COMMAND NUMBER 
 
This one-byte field contains the value of the requested command number.  The following table 
lists all the existing commands. 
 

00 

GET_PROPERTY 

Gets a property from the device 

01 

SET_PROPERTY 

Sets a property in the device 

02 

RESET_DEVICE 

Resets the device 

 
DATA LENGTH 

 

This one-byte field contains the length of the valid data contained in the Data field. 

 

 

This multi-byte field contains command data if any.  Note that the length of this field is fixed at 
22 bytes.  Valid data should be placed in the field starting at offset 2.  Any remaining data after 
the valid data should be set to zero.  This entire field must always be set even if there is no valid 

 

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