
A and
B Contro l s
The func t i on a l conf igura t i on o f each po r t i s p rog ramme d by the s y s t ems sof t
wa re .
I n e s s e nce , t he CPU " ou t p u t s " a con t ro l word to the 8 2 5 5A . The control
wor d co n t a i n s i n f o rma t i on such as "mode" , "bit se t " , " b i t re s e t " , e t c . , tha t
in i t i a l i z e s t he f unc t i ona l configura t i on o f t he
8 2 5 5 A .
E a c h o f the Co n t r o l b l ocks ( Group A a n d G roup B ) acc e p t s "commands" f rom t h e
Read/Wr i te Con t rol Log ic , r e c e i v e s "cont ro l wor d s " f rom t he i n t e rna l d a t a bus
and i s su e s t h e p rope r commands to i t s as soc i a t e d por t s .
Con t r o l Group A - P o rt
A
and P o r t C upper ( C7-C4)
Co n t r o l Group B - Port B and Por t C l owe r ( C3-CO )
The Co n t ro l Wor d Reg i s t e r can
be wr i t t e n in t o . No Read ope ra t i on of the
Con t ro l Word Reg i s t e r is a l lowe d .
P o rt A , B and C
The 8 2 5 5A cont a i n s t h r e e 8-b i t por t s ( A , B and C ) .
Al l can be conf igured in a
w ide var i e t y of f unc t i on a l charac t e r i s t i cs by t he s y s t em software but e ach has
i t s own spec ia l fea t u re s or "pe r s ona l i ty" t o fu r t he r enhance the powe r and
f l ex i b i l i t y of t he 8 2 5 5A.
Por t A . One 8-b i t data ou tput lat ch/buf f e r and one 8-b i t da t a inp u t l a t c h .
Port B . One 8-b i t da ta inpu t / ou t put l a t c h / b u f f e r and one 8-b i t d a t a i npu t
buf f e r .
Por t C . One 8-b i t da t a output l a t c h / b uf f e r and one 8-b i t data inp u t buf f e r ( no
la tch for input ) . Th i s po rt c an be d i v ide d i n t o two 4-b i t port under the mode
con t ro l .
Eac h 4-b i t por t cont a i n s a 4-b i t l a t c h and i t can be use d for the
con t ro l signal outputs and s t a t us s igna l i np u t s in conj unc t i on wi th p o r t s
A
and
B .
Mode S e l ec t i on
The r e are t h r e e ba s ic modes of ope ra t ion that can be se l ec t e d by the sys tem
s of twa re :
Mode
0
- Bas ic Inpu t / Outpu t
Mode 1
-
S t robe d Input /Ou t pu t
Mode 2 - B i-D i re c t iona l Bus
4 . 53
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 ...