Datasheet

52
AT89C51IC2
4301D–8051–02/08
Table 37. 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 Baud Rate
0 0 Shift Register F
XTAL
/12 (or F
XTAL
/6 in mode X2)
0 1 8-bit UART Variable
1 0 9-bit UART F
XTAL
/64 or F
XTAL
/32
1 1 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
o 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 flag
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 flag
Clear to acknowledge interrupt.
Set by hardware at the end of the 8th bit time in mode 0, see Figure 18. and
Figure 19. in the other modes.