Intel 8051 manual ~ J -r-r ~r~ r =fJ

8051 Architectural Specification and Functional Description

COUNTERI

GATETIMER

TIMERIRUN COUNTER

OIN MODE 3

~

G

Hn PULSE TO

SERIAL

PORT

COUNTER 1

MODE 0: 8-BIT TIMER WITH PRESCALERI 8-BIT COUNTER WITH PRESCALER-

MODE 1: 16-BIT TIMER/COUNTER

MODE 2: 8-BIT AUTO-RELOAD TIC

MODE 3: PREVENTS INCREMENTING OF TIC 1

INTERRUPT

REQUEST

J- ) -•

INT1

T1

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	XTAL1	+12	1-	~		COUNTER 0
			-	"'
					~	8-8ITTIMER
					~	(THO)
			Figure 2.5.8. Timer/Counter 1 Control and Status Flag Circuitry
• 100r11 Bit Frame		r - - - -- - - -- - -- - --- :;:R:;:;S; . - TT - ;; ----- l
•	Baud Rate Generetlon I					INTERRUPT
	from Oscillator or	I				I -___-:-__ ~~~~SMIT
	Timer 1
•	Address Frame	I				~-~-----~
	Recognition
		I		SCON
		I		(SERIAL CONTROL)
		I		CONTROL"
		I		TIMING CIRCUITRY
	g:~~~~t.,.OR- ....1
				-:-16
	TIMER 1	L ______________~~ ___ _
	OVERFLOW					RECEIVER
						RECEIVE
						DATA
				Figure 2.6. Serial Port~UART Modes 1, 2, and 3
2.1.2.4 SERIAL COMMUNICATIONS
The 8051 has a serial I/O port that is useful for serially						service the serial link. A block diagram of the serial port is
linking peripheral devices as well as multiple805ls						shown in Figure 2.6. Methods for linking UART (univer-
through standard asynchronous protocols with full-						sal asynchronous receiver / transmitter) devices are shown
duplex operatiori. The serial port also has a synchronous						in Figure 2.7 and a method for I/O expansion is shown in
mode for expansion of I/O lines using CMOS and TTL						Figure 2.8.
shift registers. This hardware serial communications
interface saves ROM code and permits a much higher						The full-duplex serial I/O port provides asynchronous
transmission rate		than could		be achieved through	o	modes to facilitate communications with standard UART
software. In response to a serial port interrupt request the						devices, such as printers and CRT terminals, or com-
CPU has only to read/write the serial port's buffer to						munications with other 8051s in multi-processor systems.

AFN-01488A-11

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