AT90SCR100 datasheet(181/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

in SCETUH register bit position 7. With COMP=1 the ETU of every character even bits is

reduced by 1 Card Clock period. As a result, the average ETU is : ETU_average = (ETU - 0.5).

One should bear in mind that the ETU counter should be programmed to deliver a faster ETU

which will be reduced by the COMP mechanism, not the other way around. This allows to reach

the required precision of the character duration specified by the ISO7816-3 standard.

Example1 : F=372, D=32 => ETU= F/D = 11.625 clock cycles.

We select ETU[10-0] = 12 , COMP=1. ETUaverage= 12 - (0.5*COMP) = 11.5

The result will be a full character duration (10 bit) = (10 - 0.107)*ETU. The EMV specification is

(10 +/- 0.2)*ETU

15.5.4

Guard Time Counter

The minimum time between the leading edge of the start bits of 2 consecutive characters trans-

mitted by the Terminal is controlled by the Guard Time counter, as described in Figure 15-4.

The Guard Time counter is an 9 bit counter. It is initialized to 001h at the start of a transmission

by the Terminal. It then increments itself at each ETU until it reaches the 9 bit value loaded into

the SCGT register. At this time a new Terminal transmission is enabled and the Guard Time

Counter stops incrementing. As soon as a new transmission starts, the Guard Time Counter is

re-initialized to 1.

Care must be taken with the Guard Time Counter which counts the duration between the leading

edges of 2 consecutive characters. This corresponds to the character duration (10 ETU) plus the

Guard Time as defined by the ISO and EMV recommendations. To program Guard Time = 2 : 2

stop bits between 2 characters which is equivalent to the minimum delay of 12 ETUs between

the leading edges of 2 consecutive characters, SCGT should be loaded with the value 12 deci-

mal. See Figure 15-2.

Figure 15-2.

Guard Time

15.5.5

Block Guard Time Counter

The Block Guard Time counter provides a way to program a minimum time between the leading

edge of the start bit of a character received from the ICC and the leading edge of the start bit of

a character sent by the terminal. ISO IEC 7816-3 and EMV recommend a fixed Block Guard

Time of 22 ETUs. The AT90SCR100 offers the possibility to extend this delay up to 512 ETUs.

The Block Guard Time is a 9 bit counter. When the Block Guard Time mode is enabled

(BGTEN=1 in SCSR register) the Block Guard Time counter is initialized to 000h at the start of a

The value of the Guard Time Counter cannot be read. Reading SCGT only gives

the minimum time between 2 characters that the Guard Time Counter allows.

Note

CHAR n+1

>= SCGT

CHAR n+2

Transmission to ICC

AT90SCR100 Datasheet(PDF) 181 Page - ATMEL Corporation

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