
38
Rev. C - 06 March, 2001
TS80C51RA2/RD2
TS83C51RB2/RC2/RD2
TS87C51RB2/RC2/RD2
Table 16. SCON Register
SCON - Serial Control Register (98h)
Reset Value = 0000 0000b
Bit addressable
7
6
5
4
3
2
1
0
FE/SM0
SM1
SM2
REN
TB8
RB8
TI
RI
Bit Number
Bit
Mnemonic
Description
7
FE
Framing Error bit (SMOD0=1)
Clear to reset the error state, not cleared by a valid stop bit.
Set by hardware when an invalid stop bit is detected.
SMOD0 must be set to enable access to the FE bit
SM0
Serial port Mode bit 0
Refer to SM1 for serial port mode selection.
SMOD0 must be cleared to enable access to the SM0 bit
6
SM1
Serial port Mode bit 1
SM0
SM1
Mode
Description
Baud Rate
0
Shift Register
FXTAL/12 (/6 in X2 mode)
0
1
8-bit UART
Variable
1
0
2
9-bit UART
FXTAL/64 or FXTAL/32 (/32, /16 in X2 mode)
1
3
9-bit UART
Variable
5
SM2
Serial port Mode 2 bit / Multiprocessor Communication Enable bit
Clear to disable multiprocessor communication feature.
Set to enable multiprocessor communication feature in mode 2 and 3, and eventually mode 1. This bit should
be cleared in mode 0.
4
REN
Reception Enable bit
Clear to disable serial reception.
Set to enable serial reception.
3
TB8
Transmitter Bit 8 / Ninth bit to transmit in modes 2 and 3.
Clear to transmit a logic 0 in the 9th bit.
Set to transmit a logic 1 in the 9th bit.
2
RB8
Receiver Bit 8 / Ninth bit received in modes 2 and 3
Cleared by hardware if 9th bit received is a logic 0.
Set by hardware if 9th bit received is a logic 1.
In mode 1, if SM2 = 0, RB8 is the received stop bit. In mode 0 RB8 is not used.
1
TI
Transmit Interrupt ag
Clear to acknowledge interrupt.
Set by hardware at the end of the 8th bit time in mode 0 or at the beginning of the stop bit in the other
modes.
0
RI
Receive Interrupt ag
Clear to acknowledge interrupt.