THE PROGRAMMABLE COMMUNICATION INTERFACE 8250-B
INS8250-B FUNCTIONAL PIN DESCRIPTION
The fo l l owing des c r i b e s the func t i on of a l l INS8 2 50 inp u t / ou tput pins . S ome o f
the se d e s c r i p t ions re fe rence i n t e rn a l c i rc u i t s .
NOTE :
In the fo l l ow ing descr i p t ions , a low re p re se n t s a l o g i c 0 ( 0 vo l t
nom ina l ) and a h i gh re p re se n t s a log i c 1 ( + 2 . 4 vo l t s nom ina l ) .
C h i p S e l e c t ( CSO , CSl ,
P i ns 1 2 - 1 4 : When CSO and CS1 are h i gh and C S 2 i s
l ow , t he c h i p i s se l e c te d . Ch ip s e l e c t i on i s comp l e te when t he decoded c h i p
se l ec t s i gna l i·s la tched w i t h an ac t ive ( l ow) Add re s s S t robe ( ADS ) i npu t . Th i s
enab l e s commun ic a t i on between t he I NS8 2 50 and t he
CPU .
Da ta Input S t robe ( DI STR ,
P i ns 2 2 and 2 1 :
When DISTR i s h i gh or D I STR
i s l ow wh i l e the chip is se l ec t e d , a l l ows the CPU to rea d s t a t u s informa t i on or
d a t a f rom a �� l ected reg i s t e r of t he INS8 2 50 .
N o t e :
Onl y an act ive DISTR o r biSTR inpu t i s re qu i re d to t ran s f e r data f rom
the INS8250 du r i ng a re a d ope rat i on . The r e fore , t ie e i t h e r the D ISTR
input pe rmane n t ly low or the DISTR input p e rmanent ly h i gh , if not u s e d .
Da ta Ou t pu t S t robe ( DOSTR , DOSTR ) , P i ns 1 9 and 1 8 : When DOSTR i s h igh o r
i s l ow wh i l e the ch ip is s e l ec t e d , a l l ows the CPU t o w r i t e da t a or con t r o l
wor d s i n t o a se l ec t e d reg i s t e r o f t he INS8 2 50 .
No t e :
Only an a c t i ve OOSTR o r OOSTR inp u t i s re qu i r e d to t rans f e r da t a to t he
INS8 250 du r i sng a wri t e op e ra t ion . There fore , t ie e i t h e r the DOSTR
input pe rmane n t ly low or t he DOSTR i npu t p e rmanen t ly h i gh , i f not u s e d .
A dd re s s S t robe ( ADS ) , P in 25 :
When low, p ro v i d e s l a tch ing for t he Reg i s t e r
Se l e c t ( AO , A1 , A2 ) and C h ip Se l e c t ( CSO , C S 1 , CS 2 ) s igna l s .
Not e :
An ac t i ve ADS input i s re qu i re d when the Reg i s t e r S e l e c t ( AO , Al , A2 )
s i g na l s are no t s t ab l e for the du ra t i on o f a rea d o r wri t e ope ra t i on .
I f n o t re qu i re d , t ie t he ADS input pe rman en t ly l ow .
Reg i s t e r S e l e c t ( AO , A1 , A2 ) , P i n s 2 6-2 8 : The s e t h r e e inpu t s a r e u s e d dur ing a
read or wr i te o pe r a t i on to s e l e c t an INS 8 2 50 reg i s t er to read f rom or wr i te
in t o a s ind i ca t e d in the tab l e be l ow . N o t e tha t the s t a t e of the D i v i sor Latch
Acce s s B i t ( DLAB ) , wh ich is t he mo s t s ig n i f icant b it of the L i ne Con t r o l
Reg i s t e r , a f f ec t s the se l ec t i on o f ce r t a i n INS8 2 50 reg i s t e r s . The DLAB mus t be
s e t h i gh by t he s y s t em s o f twa re to acce s s t he Baud Gene ra t or D iv i sor L a t c he s .
4 . 56
Содержание MKI
Страница 1: ...SERVICE TECHNICAL MANUAL VOL 1 l SVI318 328 MKI MKII COMPUTER SYSTEM SVI SPECTRAVIDEO ...
Страница 7: ...4 Remove the seven retaining screens 5 Remove the cover 2 2 ...
Страница 8: ...6 Remove the screens on the metal cover 7 Remove the metal cover 2 3 ...
Страница 9: ...To r e assemble u se the above procedures in the rever se order 2 4 ...
Страница 134: ...5 CIRCUIT SCHEMATIC AND COMPONENT LAYOUT 5 1 ...
