Intel 8xC251TB - Manual (Page 15)

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8xC251Tx Hardware Description
3.2 Special Function Register Definitions
The following describes the special function registers associated with the second serial I/O port and their bit
definitions.
3.2.1 SCON1
Address: 9AH
Reset Value: 0000 0000B
Table 6. SCON1 Special Function Register Definitions
Bit Number
Bit
Mnemonic
Function
7 FE1SM0 Framing Error Bit 1:
To Select this function, set the SMOD0 bit in the BGCON register. Set by hard-
ware to indicate an invalid stop bit. Cleared by software, not by valid frames
Second Serial I/O Port Mode Bit 0:
To select this function, clear the SMOD0 bit in the BGCON register. Software
writes to bit SM0 and SM1 to select the second serial I/O port operating
mode. Refer to SM1 bit for mode selections
6 SM1 Second Serial I/O Port Mode Bit 1:
Software write to bit SM0 and SM1 (above) to select the serial port operating
mode.
SM0 SM1 Mode Description Baud Rate
0 0 0 Shift Register Fosc/12
0 1 1 8 bit UART variable
1 0 2 9 bit UART Fosc/32* or Fosc/64*
1 1 3 9 bit UART variable
* Select by programming the SMOD0 bit in the BGCON register
5 SM2 Second Serial I/O Port Mode Bit 2:
Software writes to SM2 enable and disable the multiprocessor communica-
tion and automatic address recognition features. This allows the second
serial I/O port to differentiate between data and command frames and to rec-
ognize slave and broadcast addresses
4 REN1 Receive Enable Bit 1:
To enable reception, set this bit. To enable transmission, clear this bit
3 TB8 Transmit Bit 8:
In modes 2 and 3, software writes the ninth data bit to be transmitted to TB8.
Not used in modes 0 and 1
2 RB8 Receive Bit 8:
Mode 0: not used
Mode 1 (SM2 clear): Set or cleared by hardware to reflect the stop bit
received
Modes 2 and 3 (SM2 set): Set or cleared by hardware to reflect the ninth
data bit received
1 TI1 Second Serial I/O Port Transmit Interrupt Flag Bit:
Set by transmitter after the last data bit is transmitted. Cleared by software
0 RI1 Second Serial I/O Port Receive Interrupt Flag Bit:
Set by the receiver after the last data bit of a frame has been received.
Cleared by software