Rainbow Electronics AT89C5122 - Manual (Page 70)

70
AT8xC5122/23
4202E–SCR–06/06
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 34. Waiting Time Counter
In the so called manuel mode, the counter is loaded, if WTEN = 0, during the write of
SCWT2 register. The counter is loaded with a 32 bit word built with SCWT3 SCWT2
SCWT1 SCWT0 registers (SCWT0 contain WT[7-0] byte. WTEN is located in the
SCICR register.
When WTEN=1 and in UART mode, the counter is re-loaded at the occurence of a 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 registers 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 Ter-
minal is the maximum 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.
ETU Counter
WT Counter
Timeout
SCWT2 SCWT1 SCWT0
WT[31:0]
Load
WTEN
Start Bit
UART
Write_SCWT2
SCWT3