Sunday, January 12, 2014

CCID descriptor statistics: bVoltageSupport

Article from the serie "CCID descriptor statistics"

The bVoltageSupport field is a number value from the CCID USB descriptor:
This value indicates what voltages the CCID can supply to its slots.
It is a bitwise OR operation performed on the following values:
  • 01h 5.0V
  • 02h 3.0V
  • 04h 1.8V
Other bits are RFU.

0x0711043.31 %
0x018734.25 %
0x033714.57 %
0x02197.48 %
0x0010.39 %

The devices with bVoltageSupport = 0x00 is bogus. Even if the reader has the "Automatic ICC voltage selection" feature it should indicate the supported voltages.

Not all the possible combination are used. Readers are in one of the following categories (sorted by number of readers):
  • 0x07: 1.8V, 3V and 5V
  • 0x01: 5V only
  • 0x03: 3V and 5V
  • 0x02: 3V only
  • 0x00: bogus