TM 5-6675-318-14
k. Unlike control words, data transfer requires intervention
by the microproces-
s o r t o c o m p l e t e t h e t r a n s a c t i o n . T h i s occurs when the ATN line
is false and the
microprocessor generated signals ready (rdy), receive handshake
(rhs), new byte
available (nba), and talk handshake (ths) are used to complete
the transfer.
1.
S o u r c e (Talk) handshake sequence.
The talk logic circuitry of the HP-IB
provides the plotter with the capability to send data over the interface to the
c o n t r o l l e r . This talk function is only enabled when the plotter is addressed to
t a l k b y t h e c o n t r o l l e r . A f t e r being addressed, the HP-IB address comparator gen-
e r a t e s a my address signal and, with the decoded bits 6 and 7, which determine the
talk address, activates the talk logic circuits. The plotter talk function is
deactivated whenever the controller puts any other talk address on the bus lines.
W h e n the controller sends a valid address with DI06 false and DI07 true, the plotter
i s b e i n g a d d r e s s e d a s a t a l k e r . B i t decoder U215B and U221B decode bits 6 and 7 to
provide a pulse to clock talk flip-flop U213A. The low output (talk) from U213A
w i t h the low attention (ATN) enable the nor gate U226D to provide a data enable
( d e n ) pulse to the bus transmitters U228 and U232 through nor gate U226A.
3-123
