AT90SCR100 datasheet(182/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

character receptions from the ICC. It then increments at each ETU until it reaches the 9 bit value

loaded into shadow SCGT registers, or until it is re-initialized by the start of an new transmission

from the ICC. If the Block Guard Time counter reaches the 9 bit value loaded into shadow SCGT

registers, a transmission by the TERMINAL is enabled, and the Block Guard Time counter stops

incrementing. The Block Guard Time counter is re-initialized at the start of each terminal

transmission.

The SCGT shadow registers are loaded with the content of GT[8-0] contained in the registers

SCGT with the rising edge of the bit BGTEN in the SCSR register. See Figure 15-4.

Figure 15-3.

Block Guard Time

Figure 15-4.

Guard Time and Block Guard Time counters

To illustrate the use of Guard Time and Block Guard Time, consider the ISO/IEC7816-3 recom-

mendation : Guard Time = 2 (minimum delay between 2 consecutive characters sent by the

Terminal = 12 ETUs), and Block Guard Time = 22 ETUs.

After a smart Card Reset

• Write ‘00’ decimal in SCGTH, Write ‘22’ decimal in SCGTL

• Set BGTEN in SCSR (BGTEN was 0 before as a result of the smart card reset)

• Write ‘12’ decimal in SCGTL

Now the Guard Time and Block Guard Time are properly initialized. The TERMINAL will insure a

minimun 12 ETUs between 2 leading edges of 2 consecutive characters transmitted. The TER-

MINAL will also insure a minimum of 22 ETUs between the leading edge of a character sent by

CHAR 1

>= SCGT

CHAR 2

CHAR n

CHAR 1

CHAR 2

Reception from ICC

Transmission to ICC

>= Block Guard Time

Write “Block Guard Time” in SCGT

the value to the shadow SCGT register

Write SCGT with a value

for Guard Time

Guard Time Counter

Block Guard Time Counter

Comparator

Shadow SCGTH

Shadow SCGTL

SCGTH

SCGTL

ETU Counter

9 bits

Transmit Enable

9 bits

GT[8..0]

9 bits

AT90SCR100 Datasheet(PDF) 182 Page - ATMEL Corporation

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