AT90SCR100 datasheet(183/433 Pages) ATMEL

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TPR0327AY–SMS–30Jan09

AT90SCR100

the ICC, and the leading edge of a character sent by the TERMINAL. There is no need to write

SCGT again and again.

15.5.6

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 15-5.

When the WT counter times out, an interrupt is generated and the SCIB function is locked:

reception and emission are disabled. It can be enabled by resetting the macro or reloading the

counter.

The Waiting Time Counter can be used in T=0 protocol for the Work Waiting Time. It can be

used in T=1 protocol for the Character Waiting Time and for the Block Waiting Time. See the

detailed explanation below.

Figure 15-5.

Waiting Time Counter

In the so called manual mode, the counter is loaded, if WTEN = 0, during the write of SCWT2

registers (SCWT0 contains WT[7-0] bytes. WTEN is located in the SCICR register.

When WTEN=1 and in UART mode, the counter is re-loaded at each start bit. This mode will be

detailed below in T=0 protocol and T=1 protocol.

In manual mode, the WTEN signal controls the start of the counter (rising edge) and the stop of

the counter (falling edge). After a timeout of the counter, a falling edge on WTEN, a reload of

SCWT2 and a rising edge of WTEN are necessary to start again the counter and to release the

SCIB macro. The reload of SCWT2 transfers all SCWT0, SCWT1, SCWT2 and SCWT3 regis-

ters to the WT counter.

In UART mode there is an automatic load on the start bit detection. This automatic load is very

useful for changing on-the-fly the timeout value since there is a register to hold the load value.

This is the case for T=1 protocol.

In T=0 protocol the maximun interval between the start leading edge of any character sent by

the ICC and the start of the previous character sent by either the ICC or the Terminal is the max-

imum Work Waiting Time. The Work Waiting Time shall not exceed 960*D*WI ETUs with D and

WI parameters are returned by the field TA1 and TC2 respectively in the Answer To Reset

(ATR). This is the value the user shall write in the SCWT0,1,2,3 register. This value will be

reloaded in the Waiting Time counter every start bit.

Guard Time Counter

Timeout

Load

WT [31..0]

ETU Counter

WTEN

Write SCWT2

Uart

Start Bit

SCWT3

SCWT2

SCWT1

SCWT0

AT90SCR100 Datasheet(PDF) 183 Page - ATMEL Corporation

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