intd.
HARDWARE DESCRIPTION OFTHE 8051,8052 AND 80C51
l++
+12
TR2
nEmAO
-R 2
llslEmnlWr
Max PfN
axaNa
270252-13
Figure 13. Timer 2 in Auto-Reload Mode
(MSB) (LSB)
SMO
SM1 SM2
REN I TB8 I RSS ] n I RI
Where SMO, SM1 epeeify the aefial pommode, as follows:
● TSS ie the Sthdate bifthetwill be
SMO aMl mode Deeerfpnorl
Scud Rate
bans- in Modaa2 end3. % or
o
0
0
Shiftragiatar f=flz
dear byaoftwareaa rtaairad.
o
1
1 S-bifUART
vadable
● RSS
1
inModes 2and 3, iatha Sthdata bit
o
2
9-bitUART f-/s4
thatwes received. In Mode 1, ifSM2
or
= O,RSS iethe atopbitthet wea
f=,/32
received. In MOdeO,RS3 is rrotuaed.
1
1
3
9-btuARTvenable
● TI
iewenemifirstarruptflag.Set by
s SM2
enebleethe muftipromaeor
hardsrareatthe endofttw8th bittime
communieatfonfeature in Modes 2
inM*O, oratthe beginningof the
and 3.InM*20r3, ifSM2isaetto
*P bitinthe offwrrnodes,inany
1 than RI willnotbaactf.mtad ifthe
aerieffmnamieaion.Muetbecleared
received 3th date bit(R*) iaO. In
Mode 1, if SM2 = 1 thenRI willnot
byaoftware.
baatited ifavalid stopbhwea not
● RI
isreceive irsferruptflag.Sat by
recefvad.In Mode O,SM2 ahouldbe
herdwareatthe endofthesth bittime
o.
inMode O,or helfweythrcrughthe atop
● REN
enableeaeriel reqstion. %by
b4ttirrwinthe othermodes,inany
eoftwareto enable raoaption.Clear
serialrecefdkm
(exoepta8a SM2).
byeoftwaretodieeble raee+stkm
Muafbe Cia byeoftwere.
—. . ----- - . . — — —
Figure 14. SCON:Serial Port Control Register
The baudrate in ModeOis tlxed:
2SMOD
Mode2
BaudRate=
~X(Oscillator Frequency)
OscillatorFrequency
ModeOBaudRate =
12 In the 8051.the baud rateain Modes1and 3 are deter-
minedbythe Timer 1overflowrate. In the 8052,these
The baud rate in Mode 2 dependeon the value of bit baud ratea earsbe determinedbyTimer 1,or by Timer
SMODin SpecialFunctionRegisterPCON.If SMOD
2, or by both (one for transmit end the other for re-
= O(whichis the valueon reset),the baudrate % the
eeive).
oaeillatorfrequency.If SMOD = 1, the baud rate ie
%2the oscillatorfrequency.
3-15
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