Rainbow Electronics T89C5121 - Manual (Page 90)

90
A/T8xC5121
4164G–SCR–07/06
Framing Error Detection
(Modes 1, 2 and 3) Framing error detection is provided for the three asynchronous modes. To enable the
framing bit error detection feature, set SMOD0 bit in PCON register as shown in
Figure 46.
When this feature is enabled, the receiver checks each incoming data frame for a valid
stop bit. An invalid stop bit may result from noise on the serial lines or from simultaneous
transmission by two devices. If a valid stop bit is not found, the software sets FE bit in
SCON register.
Software may examine FE bit after each reception to check for data errors. Once set,
only software or a chip reset clear FE bit. Subsequently received frames with valid stop
bits cannot clear FE bit. When the framing error detection feature is enabled, RI rises on
stop bit instead of the last data bit as detailed in Figure 36.
Figure 46. Framing Error Block Diagram
Baud Rate Selection (Modes 1
and 3) In modes 1 and 3, the Baud Rate is derived either from the Timer 1 or the Internal Baud
Rate Generator and allows different baud rate in reception and transmission.
As shown in Figure 47 the selection is done using RBCK and TBCK bits in BDRCON
register.
Figure 48 gives the baud rate calculation formulas for each baud rate source while
Table 65 details Internal Baud Rate Generator configuration for different peripheral
clock frequencies and giving baud rates closer to the standard baud rates.
Figure 47. Baud Rate Source Selection (Modes 1 and 3)
Figure 48. Baud Rate Formulas (Modes 1 and 3)
SM0
1
0
SMOD0
PCON.6
SM0/FE
SCON.7
Framing Error
Controller
FE
0
1
RBCK
BDRCON.2
T1
CLOCK
To Serial
IBRG
CLOCK
Reception Port
0
1
TBCK
BDRCON.3
T1
CLOCK
To serial
IBRG
CLOCK
Transmission Port
ч 16 ч 16
Baud_Rate =
6 (1-SPD) ⋅ 32 ⋅ (256 -BRL)
2 SMOD1 ⋅
F
PER
BRL = 256
-
6 (1-SPD ) ⋅ 32 ⋅ Baud_Rate
2 SMOD1 ⋅ F
PER
Baud_Rate =
6 ⋅ 32 ⋅ (256 -TH1)
2 SMOD1 ⋅ F
PER
TH1 = 256 -
192 ⋅ Baud_Rate
2 SMOD1 ⋅
F
PER
a. BRG Formula b. T1 Formula