Spectravideo MKI, Сервисное – Техническое руководство

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Tab l es 3 and
4
i l l us t rate the use of
die BS'ud
Rate Gener tor with crysta l
f re quencies of
1 . 8432 MHz
and
3 . 0 7 2 MHz
respect ive ly . For baud rates of
38400
and be low the e r ror ob ta ined i s minima l . The accuracy of the des i re d baud rate
is dependent on t he crys t a l f requency chosen .
Not e : The max imum operat ing f re quency
Howeve r , when us ing divisors of
is e qual to the divi sor in
MHz .
then t he maximum f requency i s
1
rate be greater than 56K Baud .
Line S ta tus
of the Baud Gene rator is
3 . 1 MHz .
3
and be low , the maximum f requency
For example , if the divisor is
1 ,
MHz .
In no case shou ld the data
This 8-b it reg i s t e r provides stat us informa t ion to the CPU conce rning the data
t ransfe r . The contents of the Line S tatus Reg ister are ind icated in tab le
2
and are descr ibed be low .
B i t 0 : Th is b i t is the receer Dat a Ready ( DR ) ind icator . B i t
0
i s s e t t o a
log ic 1 wheneve r a comp le te incoming cha rac ter has been rece ived and t rans­
ferred into the Receive r Buf fer Reg i s te r . B i t
0
may be re set t o a log ic
0
e i ther by t he CPU reading the da t� in t he Rece iver Buffer Reg i s ter or by
wr i t ing a log ic
0
into it f rom the CPU .
B i t 1 : This b i t is the Ove rrun E r ror { OE ) ind icat or. B i t
1
indicates t hat
dat a in the Rece i ver Buf fer Reg ister was no t read by the CPU be fore the nex t
character was t rans f e r re d into t he Rece iver Bu ffer Reg i s te r , the reby des t roying
the p revious cha racte r . The OE indi ca tor is re set wheneve r the CPU reads the
conten ts of t he L i ne S t atus Re
g
i s t e r .
Bi t 2 : Thi s b i t is the Par ity Error ( PE ) indicat or . B i t 2 ind icates tha t the
rece i ved da ta cha racter does not have t he correct even or odd par i t y , as
se l e c t e d by the even-pa ri t y-se l ect b i t . The PE b i t is set to a log ic
1
upon
de te c t i on of a par ity e rror and is reset to a log ic
0
whenever the CPU reads
the cont ents of the L ine S ta tus Registe r .
4
•.
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