AT89C5122D-RDRUM datasheet(67/208 Pages) ATMEL

67 / 208 page

AT83R5122, AT8xC5122/23

4202F–SCR–07/2008

Figure 31.

Block Guard Time.

Figure 32.

Guard Time and Block Guard Time counters

To illustrate the use of Guard Time and Block Guard Time, let us consider the

ISO/IEC7816-3 recommendation : Guard Time = 2 (minimum delay between 2 consecu-

tive characters sent by the Terminal = 12 ETUs), and Block Guard Time = 22 ETUs.

After A smart Card Reset

–

Write 00decimal in SCGT1, Write 21decimal in SCGT0

–

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

reset)

–

Write 12decimal in SCGT0

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 trans-

mitted. The TERMINAL will also insure a minimum of 22 ETUs between the leading

edge of a character sent by the ICC, and the leading edge of a character sent by the

TERMINAL. There is no need to write SCGT1,0 again and again.

Waiting Time (WT) Counter

The WT counter is a 32 bits down counter which can be loaded with the value contained

in the SCWT3, SCWT2, SCWT1, SCWT0 registers. Its main purpose is timeout signal

generation. It is 32 bits wide and is decremented at the ETU rate. see Figure 33.

CHAR 1

CHAR 2

CHAR n

CHAR n+1

CHAR n+2

CHAR n+3

>= Block Guard Time

>= SCGT

RECEPTION from ICC

TRANSMISSION to ICC

Write “Block Guard Time” in SCGT1,0

Write SCGT1,0 with

and set BGTEN to transfer the value to the

shadow SCGT1,0 registers

a value for Guard Time

ETU Counter

Block Guard Time Counter

Enable

SCGT1

SCGT0

9 bits

Guard Time Counter

GT[8:0]

Shadow SCGT1 ,Shadow SCGT0

9 bits

Comparator

transmit

Comparator

9 bits

Enable

transmit

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