W79E225A Datasheet, PDF (144/200 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/227A Data Sheet
16.4 Mode 3
This mode is the same as Mode 2, except that the baud rate is programmable. The program must
select the mode and baud rate in SCON before any communication can take place. Timer 1 should be
initialized if Mode 1 or Mode 3 will be used.
SM0
0
0
1
1
SM1
0
1
0
1
Figure 16-4 Serial Port Mode 3
MODE TYPE
0
Synch.
1
Asynch.
BAUD
CLOCK
4 or 12 OSC
Timer 1 or 2
FRAME
SIZE
8 bits
10 bits
2
Asynch. 32 or 64 OSC 11 bits
3
Asynch. Timer 1 or 2 11 bits
Table 16-1: Serial Ports Modes
START
BIT
No
1
1
1
STOP
BIT
No
1
1
1
9TH BIT
FUNCTION
None
None
0, 1
0, 1
16.5 Framing Error Detection
A frame error occurs when a valid stop bit is not detected. This could indicate incorrect serial data
communication. Typically, a frame error is due to noise or contention on the serial communication line.
The W79E225/227 has the ability to detect framing errors and set a flag that can be checked by
software.
The frame error FE (FE_1) bit is located in SCON.7. This bit is SM0 in the standard 8051/52 family,
but, in the W79E225/227, it serves a dual function and is called SM0/FE. There are actually two
separate flags, SM0 and FE. The flag that is actually accessed as SCON.7 is determined by SMOD0
(PCON.6). When SMOD0 is set to 1, the FE flag is accessed. When SMOD0 is set to 0, the SM0 flag
is accessed.
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Publication Release Date: December 14, 2007
Revision A2.0