TM 5-6675-323-14
(1) data bus - 8 s i g n a l l i n e s - D I 0 1 t h r o u g h D I 0 8 ,
(2) data transfer control - 3 signal lines - (Handshake),
(3) interface management - 5 signal lines.
d. The data bus transfers 8-bit data or control words between
the controller and
t h e p l o t t e r . The words are in bit-parallel byte-serial form. The
words are trans-
f e r r e d b i d i r e c t i o n a l l y . The three data transfer control lines, or
handshake lines,
are used to control the transfer of information on the data bus.
These lines are
identified as follows:
( 1 ) Data valid (DAV) - u s e d to indicate that valid i n f o r m a t i o n
is
available
on the data lines.
( 2 ) Not ready for data (NRFD) - used to indicate t h e r e a d i n e s s o f t h e p l o t t e r
to
accept information.
( 3 ) Not data accepted (NDAC) - u s e d t o i n d i c a t e t h e a c c e p t a n c e o f i n f o r m a t i o n
by the plotter.
e. The five interface management lines are used to provide an orderly flow of
information across the interface bus.
In the operation of the 9872C plotter on the
interface bus, the remote enable (REN) is not used. The five interface management
lines are identified as follows:
( 1 ) A t t e n t i o n ( A T N ) - used by the controller to specify how data on the 010
signal lines are to be interpreted (command, data, or parallel poll response), and
which devices on the bus must respond to the data.
( 2 ) Service request (SRQ) - u s e d t o i n d i c a t e t h a t t h e p l o t t e r n e e d s a t t e n t i o n
and to request an interruption of the current sequence of events.
( 3 ) I n t e r f a c e c l e a r ( I F C ) - used by t h e c o n t r o l l e r t o p l a c e t h e b u s i n a
known
quiescent condition.
( 4 ) E n d o r i d e n t i f y (EOI) - used by a t a l k e r t o i n d i c a t e t h e e n d o f a m u l t i -
p i e - b y t e t r a n s f e r s e q u e n c e or, in conjunction w i t h A T N , t o e x e c u t e a p o l l i n g
sequence.
(5) Remote enable (REN) - not used.
f.
Positive true logic is used within the plotter circuitry. A capital letter N
before a mnemonic, such as NRFD, shows an inversion for that line.
Power up. W h e n p o w e r i s a p p l i e d t o t h e p l o t t e r , a r e s e t s i g n a l i s g e n e r a t e d
in the power supply. T h i s r e s e t p u l s e i s u s e d t o c l e a r f l i p - f l o p s t h u s s e t t i n g t h e
p l o t t e r t o a k n o w n c o n d i t i o n . T h e NDAC and NRFD lines to the controller are set
p a s s i v e t r u e i n d i c a t i n g t h i s i d l e c o n d i t i o n . T h e reset pulse can also be generated
by pressing the RESET switch S5 on the main PCA A2.
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