3.3.23. SCICHGUARD: [8] (+0x58)

SCICHGUARD is the character to character extra guard time register. It defines the extra guard time that will be added to the minimum duration between leading edges of the start bits of two consecutive characters, for subsequent communication from the interface to the Smart Card.

The SCICHGUARD value is derived from the TC1 value that is extracted from the ATR character stream. Table 3.25 shows bit assignments for SCICHGUARD.

Table 3.25. SCICHGUARD register read/write bits

Bits

Name

Type

Function

7:0

SCICHGUARD

Read/write

Defines the minimum duration between the leading edges of the start bits of two consecutive characters for subsequent communication from the interface to the Smart Card.

The TC1 value can be between 0 and 255. The software must read the TC1 value and program the SCICHGUARD register as described in Table 3.26 to provide the resultant guard time in etus.

Table 3.26. SCIVALUE register read/write bits

ATR TC1 value

SCICHGUARD value

Resultant guard time (etus)

T0

T1

T0

T1

0 =<TC1<255

TC1

TC1 + 1

TC1 + 12

TC1 + 11

255

0

0

12

11

A TC1 value of 255 indicates that the minimum delay between the start leading edges of two consecutive characters will be 12 etus if T=0, or 11 etus if T=1 is to be used.

Note

The TXNAK bit value in the SCICR0 register is used by the interface hardware to determine whether T0 or T1 protocol is in operation.

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