Question

(1 point) Write an assembly program for the 8051 to transfer the letter 'Z' serially at 2400 baud, continuously.

Please explain!

Answer 1

8051 Assembly Program:

MOV TMOD,#20H ;timer 1, mode 2

MOV TH1, #-12 ;2400 baud rate

MOV SCON,#50H ;8-bit, 1 stop, REN enabled

SETB TR1 ;start timer 1

AGAIN : MOV SBUF,#"Z" ;letter "Z" to be transferred

HERE : JNB TI, HERE ;wait for last bit

CLR TI ;clear TI for next char

SJMP AGAIN ;Keep sending Z (Continously)

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Explanation:

Baud Rates in the 8051:

• Timer 1, mode 2 (8-bit, auto-reload)
• Define TH1 to set the baud rate.
XTAL = 11.0592 MHz
The system frequency = 11.0592 MHz / 12 = 921.6 kHz
Timer 1 has 921.6 kHz/ 32 = 28,800 Hz as source.
TH1=FDH means that UART sends a bit every 12 timer source.
Baud rate = 28,800/12= 2,400Hz where -12 (or F4 in HEX) is loaded into TH1.

Registers used in Serial Transfer Circuit:

SUBF (Serial data buffer)
SCON (Serial control register)

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