ATR statistics: TA4

Article from the series "ATR statistics"

TA4

The first TA for T=15 encodes the clock stop indicator (X) and the class indicator (Y). The default values are X = "clock stop not supported" and Y = "only class A supported".

bits 8 and 7 indicate whether the card supports clock stop (≠ 00) or not (= 00) and, when supported, which state is preferred on the electrical circuit CLK when the clock is stopped.

• 00b: Clock stop not supported
• 01b: State L
• 10b: State H
• 11b: No preference

bits 6 to 1 indicate the classes of operating conditions accepted by the card. Each bit represents a class: bit 1 for class A, bit 2 for class B and bit 3 for class C.

• 00 0001b: A only
• 00 0010b: B only
• 00 0100b: C only
• 00 0011b: A and B
• 00 0110b: B and C
• 00 0111b: A, B and C
• Any other value: RFU

TA4	#	%
	2009	96.96 %
0x03	27	1.30 %
0x83	15	0.72 %
0xC3	12	0.58 %
0x07	6	0.29 %
0x43	2	0.10 %
0xC7	1	0.05 %

Clock stop	#	%
not supported	33	52.38 %
state L	2	3.17 %
state H	15	23.81 %
no preference	13	20.63 %

The class defines the current voltage the card can use:

• class A: 5 V
• class B: 3 V
• class C: 1.8 V

Some readers can't provide a tension of 5V. For example the Gemalto CT1100 reader does only provide 3 V. The default value for TA₄ is "only class A supported". Some (old) cards require a voltage of 5 V to work and will not work with a CT1100. That can be surprising.

Class	#	%
A & B	56	88.89 %
A & B & C	7	11.11 %