8051 Special Function Registers

PCON SFR
Bit	Symbol
7	SMOD
6	--
5	---
4	---
3	GF1
2	GF0
1	PD
0	IDL

SCON SFR
Bit	Symbol
7	SM0
6	SM1
5	SM2
4	REN
3	TB8
2	RB8
1	TI
0	RI

SM0	SM1	Mode	Description
0	0	0	shift register
0	1	1	8-bit variable baud rate UART
1	0	2	9-bit UART
1	1	3	9-bit variable baud rate UART

TMOD SFR
Bit	Name	Timer
7	Gate	1
6	C/T-bar	1
5	M1	1
4	M0	1
3	Gate	0
2	C/T-bar	0
1	M1	0
0	M0	0

M1	M0	Mode	Description
0	0	0	13-bit timer mode
0	1	1	16-bit timer mode
1	0	2	8-bit auto-reload mode
1	1	3	Split timer mode

TCON SFR
Bit	Symbol	Description
7	TF1	Timer 1 overflow
6	TR1	Timer 1 start/stop
5	TF0	Timer 0 overflow
4	TR0	Timer 0 start/stop
3	IE1	External interrupt 1 flag
2	IT1	External interrupt 1 type: 0 = low-level; 1 = edge
1	IE0	External interrupt 0 flag
0	IT0	External interrupt 0 type: 0 = low-level; 1 = edge

Vector Table
Interrupt	Flag	Vector
System reset	RST	0000H
External interrupt 0	IE0	0003H
Timer 0	TF0	000BH
External interrupt 1	IE1	0013H
Timer 1	TF1	001BH
Serial port	RI or TI	0023H

Interrupt Enable SFR		1 = enable 0 = disable
Symbol	Bit Number	Description
EA	7	Enable/disable all interrupts.
--	6
--	5
ES	4	Enable/disable serial port interrupts.
ET1	3	Enable/disable timer 1 interrupt.
EX1	2	Enable/disable external 1.
ET0	1	Enable/disable timer 0 interrupt.
EX0	0	Enable/disable external 0 interrupt.

Interrupt Priority SFR		1= high 0 = low
Symbol	Bit Number	Description
--	7
--	6
--	5
PS	4	Serial port
PT1	3	Timer 1
PX1	2	External interrupt 1
PT0	1	Timer 0
PX0	0	External interrupt 0