TM 5-6675-320-14
k. Unlike control words, data transfer requires intervention by the microproces-
sor to complete the transaction. This 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.
Source (Talk) handshake sequence.
T h e t a l k l o g i c c i r c u i t r y o f t h e H P - I B
provides the plotter with the capability to send data over the interface to the
controller. This talk function is only enabled when the plotter is addressed to
talk by the controller. After being addressed, the HP-IB address comparator gen-
erates a my address signal and, with the decoded bits 6 and 7, which determine the
t a l k a d d r e s s , a c t i v a t e s t h e t a l k l o g i c c i r c u i t s . T h e p l o t t e r t a l k f u n c t i o n is
deactivated whenever the controller puts any other talk address on the bus lines.
When the controller sends a valid address with DI06 false and DI07 true, the plotter
is being addressed as a talker. Bit decoder U215B and U221B decode bits 6 and 7 to
provide a pulse to clock talk flip-flop U213A. The low Q output (talkj from U213A
with the low attention (ATN) enable the nor gate U226D to provide a data enable
(den) pulse to the bus transmitters U228 and U232 through nor gate U226A.
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