ST7SCR datasheet(58/102 Pages) STMICROELECTRONICS

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ST7SCR

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SMARTCARD INTERFACE (Cont’d)

Waiting Time Counter

The Waiting Time counter is a 24-bit counter used

to generate a timeout signal.

The elementary time unit counter acts as a pres-

caler to the Waiting Time counter which is incre-

mented at the etu rate.

The Waiting Time Counter can be used in both

UART mode and Manual mode and acts in differ-

ent ways depending on the selected mode.

The CRDWT2, CRDWT1 and CRDWT0 are load

registers only, the counter itself is not directly ac-

cessible.

UART Mode

The load conditions are either:

– A Start bit is detected while UART bit =1 and the

WTEN bit =1.

– A write access to the CRDWT2 register is per-

formed while the UART bit = 1 and the WTEN bit

= 0. In this case, the Waiting Time counter can be

used as a general purpose timer.

In UART mode, if the WTEN bit of the CRDCR reg-

ister is set, the counter is loaded automatically on

start bit detection. Software can change the time

out value on-the-fly by writing to the

CRDWT registers. For example, in T=1 mode,

software must load the Block Waiting Time (BWT)

time-out in the CRDWT registers before the start

bit of the last transmitted character.

Then, after transmission of this last character, sig-

nalled by the TXC interrupt, software must write

the CWT value (Character Waiting Time) in the

CRDWT registers. See example in Figure 31.

Manual mode

The load conditions are:

– A write access to the CRDWT2 register is per-

formed while the UART bit = 0 and the WTEN bit

= 0

In Manual mode, if the WTEN bit of the CRDCR

pose timer. The timer is loaded when a write ac-

cess to the CRDWT2 register occurs. The timer

starts when the WTEN bit = 1.

12.4.3.4 Interrupt generator

The Smartcard Interface has 2 interrupt vectors:

– Card Insertion/Removal Interrupt

– CRD Interrupt

The CRD interrupt is cleared when software reads

the CRDIPR register. The Card Insertion/Removal

is an external interrupt and is cleared automatical-

ly by hardware at the end of the interrupt service

routine (IRET instruction).

If an interrupt occurs while the CRDIPR register is

being read, the corresponding bit will be set by

hardware after the read access is done.

Figure 31. Waiting Time Counter Example

BWT

CWT

Reader

Smartcard

Firmware must program BWT

Firmware must program CWT

TXC Interrupt

Start bit

Waiting Time Counter

loaded on start bit

CHAR0

CHAR1

CHARn

CHAR0

CHAR1

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