AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 69

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Waiting Time (WT) Counter
4202D–SCR–06/05
Enable
transmit
ETU Counter
Figure 32. Block Guard Time.
Figure 33. 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
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.
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 34.
Comparator
–
–
–
CHAR 1
Guard Time Counter
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
RECEPTION from ICC
CHAR 2
9 bits
9 bits
Shadow SCGT1 ,Shadow SCGT0
Write “Block Guard Time” in SCGT1,0
and set BGTEN to transfer the value to the
shadow SCGT1,0 registers
SCGT1
CHAR n
>= Block Guard Time
9 bits
GT[8:0]
Write SCGT1,0 with
a value for Guard Time
SCGT0
Block Guard Time Counter
CHAR n+1
>= SCGT
TRANSMISSION to ICC
CHAR n+2
9 bits
Comparator
CHAR n+3
Enable
transmit
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