Rs-232-C/Ccitt V.24 Interface Circuits - HP 7475A Service Manual

Model 7475A
1/0
7475-A-13-1A
LINE DRIVERS/
DS~~A
6
READY
CLitR 5
SEND
L~NEgl~~~L
8
DETECTOR
TE~~i~AL
20
READY
RECEIVED 3
DATA
s~~~~~~~Y16
DATA
RECEIVERS
0
0
0
0
REQUEST~
TO SEND
'--...J '\/
FA
07
FA 06
FA
05
FA
04
5
EI00
Section VI
INTERNAL
DATA BUS
ACIA
Rrs
R/W
13
R EAD/iiVRITE
E
14
1 MHz
2
RXD
3
RX CLK
BAUD RATE
TX CLK
4
CLOCK
11
A6
A13
CS1
10
A15
CS0
8
VMA
15
07
U13
16
06
17
05
6 TXD
18
04
INTERNAL
19
DJ
DATA BUS
20
02
21
01
22
00
Figure 6-2. RS-232-C/CCITT V.24 Interface Circuits
6-20. The five interface management lines are used to
provide an orderly flow of information accross the inter-
face bus. The lines are identified as follows:
a. ATTENTION (ATN) - Used by the controller to
specify how data on the DIO signal lines are to
be interpreted, (command, data, or parallel poll
response) and which devices on the bus must
respond to the data.
b. SERVICE REQUEST (SRQ) - Used to indicate
that the plotter needs attention and to request an
interruption of the current sequence of events.
c. INTERFACE CLEAR (IFC) - Used by the con-
troller to place the bus in a known quiescent
condition.
d. END OR IDENTIFY (EOI) - Used by a talker to
indicate the end of a multiple-byte transfer
sequence or, in conjunction with ATN to execute
a polling sequence.
e. REMOTE ENABLE (REN) - Used to enable a
remote control mode.
6-21. Positive true logic is used within the plotter cir-
cuitry. Therefore a positive false NRFD on the HP-IB
bus will
be
converted to a positive true RFD within the
plotter.
6-22. When the HP-IB interface IC U12 receives a RESET
pulse from the microprocessor U13 it sets the DAC and
RFD lines passive true, indicating the ready condition.
The controller will set ATN true indicating a bus message
or address, and put the device address on data lines
DIOI through DI05. The interface chip compares the
address on the bus with the setting of the HP-IB address
switch read at power up. If the address is valid, the HP-
IB chip will then decode the lines DI06 and DI07, to
determine ifthe 7475A is being addressed as an acceptor
(listener) or source (talker). When the controller sends a
valid address with DI06 true and DI07 false, the plotter
is being addressed as a listener. When the controller is
6-3