Hi all,

Can any one tell me how to use the UART for various baud rates for 89C52 Which runs with clock of 24MHz. I've googled but couldn't get it. please help me.

regards,
saha

 

89C52's are getting pretty obsolete these days. A very quick Google check turned up this - http://www.atmel.com/dyn/resources/prod_documents/doc0313.pdf - which has inside very exact methods for setting the baud rate.

 

Hi all,
Thanks a lot, i tried a lot and got a solution. As a simple logic if we configure a 89C52 to run at 300bps, by replacing the 12MHz with 24MHz we can get the serial transmission to be double the speed that is 600bps. With this crude logic i checked by prgramming and replacing it worked. hence just giving the reload values. hope will be of use to some one.

BAUD RATEs a,b,c,d

(a) - FOR 89C52 CLK 12MHz without doubling baud rate

(b) - FOR 89C52 CLK 12MHz with doubling baud rate .
MOV PCON,#080h

(c) - FOR 89C52 CLK 24MHz without doubling baud rate

(d) - FOR 89C52 CLK 24MHz with doubling baud rate .
MOV PCON,#080h

(e) TH1 -AUTO RELOAD VALUE


12MHz 24MHz TH1

(a) (b) (c) (d) (e)
; 300 600 600 1200 98h
; 1200 2400 2400 4800 E8h
; 2400 4800 4800 9600 F4h
; 4800 9600 9600 19200 FAh
; 9600 19200 19200 38400 FDh


of course 89c52 are becoming obsolete but there are countless systems which run on these processors and undoubtedly the designers are CRAMMING the hardware logic in it.

regards,
saha

 

Example: 9600 bps on 24 MHz

9600 x 32 = 307200

Interval between overflow = 1/307200 = 3.255 us

Timer run rate = 1(24000000/12) = 0.5 us

Count = 3.255/0.5 = 6 (there will be baud rate error)

(TL1) = 255 - 6 = 249 (F9h)

To avoid baud rate error, use 22.1184 MHz crystal.

MOV TMOD,#20H
MOV SCON,#50H
MOV TH1,#0F9H
SETB TR1