TM 5-6675-320-14
(1) data bus - 8 signal lines - DI01 through DI08,
(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 . T h e w o r d s a r e i n b i t - p a r a l l e l b y t e - s e r i a l f o r m . T h e w o r d s a r e t r a n s-
f e r r e d b i d i r e c t i o n a l l y . T h e t h r e e d a t a t r a n s f e r c o n t r o l l i n e s , o r h a n d s h a k e l i n e s,
are used to control the transfer of information on the data bus. These lines are
i d e n t i f i e d a s f o l l o w s:
(1) Data valid (DAV) -
u s e d t o i n d i c a t e t h a t v a l i d i n f o r m a t i o n i s a v a i l a b le
on the data lines .
(2) Not ready for data (NRFD) -
used to indicate the readiness of the plotter
to accept information.
(3) Not data accepted (NDAC) - used to indicate the acceptance of information
b y t h e p l o t t e r .
e.
The five interface management lines are used to 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
l i n e s a r e i d e n t i f i e d a s f o l l o w s:
(1) Attention (ATN) - used by the controller to specify how data on the DI0
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) -
used to indicate that the plotter needs attention
and to request an interruption of the current sequence of events.
( 3 ) I n t e r f a c e c l e ar
known quiescent condition.
(4) End or identify
pie-byte transfer sequence
sequence.
(IFC) - used by the controller to place the bus in a
(EOI) -
used by a talker to indicate the end of a multi-
or, in conjunction with ATN, to execute a polling
f .
before
g.
in the
(5) Remote enable (REN) - not used.
P o s i t i v e t r u e l o g i c i s u s e d w i t h i n t h e p l o t t e r c i r c u i t r y . A c a p i t a l l e t t e r N
a mnemonic, such as NRFD, shows an inversion for that line.
Power up. When power is applied to the plotter, a reset signal is generated
p o w e r s u p p l y . 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 he
plotter to a known condition. The NDAC and NRFD lines to the controller are set
passive true indicating this idle condition. The reset pulse can also be generated
by pressing the RESET switch S5 on the main PCA A2.
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