Connecting The Rs-232-C Interface - HP 7470A Interfacing And Programming Manual

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deration
The rear-panel switch labeled Y/D should be set to D. If it is set to Y, the
plotter must receive a plotter on instruction, ESC . ( or ESC . Y, before
it will respond to other commands from the terminal. The terminal
should be set to half duplex in order to view the characters being sent
to the plotter. Plotter output will be displayed on the terminal. The
following diagram shows plotter operation when in the programmed-on
state in a terminal-only environment.
PLOTTER
4 i
OUTPUT
PLOTTER
INSTRUCTIONS
Terminal-only Environment, Programmed On
onnecting the RS-232-C Interface
The 7470 plotter interfaces to the RS-232-C communications lines
) through a standard 25-pin female connector mounted on the back of the
plotter. The 7470 is capable of operating in a three-wire (transmit,
)
receive, ground) configuration.
In hardwired handshake operation, the Data Terminal Ready line (pin
20 of the connector on the plotter) is used to monitor the space in the
buffer available for input. The plotter outputs data when requested
(refer to Hardwire Handshake in this chapter).
If you are fabricating the cable assembly, the connector should be a
25-pin type " D " subminiature CINCH DBC-25P plug or equivalent.
Connector pin allocations for the three-wire configuration are identified
and described in the following table.
JK 10 RS-232-C/CCITT V.24 INTERFACING
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Minimum Interface Connector Pin Allocations
P i n No.
2
3
7
RS-232-C
BA
(TDATA)
BB
(RDATA)
AB
(SGND)
C C I T T V.24
103
104
102
F u n c t i o n / S i g n a l Level
Data line from plotter
High = ON = "0" = +12 V
= SPACE
Low = OFF = " l " = - 1 2 V
= MARK
Data line to plotter
High = ON = "0" = +3 V
to +25 V
Low = OFF = " 1 " = - 3 V
to - 2 5 V
Signal ground (Return
line)
I
In addition to the minimum requirements for communication, six more
lines are connected as shown in the following table. These lines are
required to implement full duplex communication, intermediate baud
rate, hardwired handshake mode, and monitor mode. All remaining
pins make no internal connection.
Pins 14 and 16 are wired in the special Y-cable, available as Option 16,
to implement monitor mode. The Y-cable schematic is shown below.
NOTE: Hardwire handshake c a n n o t be used to prevent buffer overflow
when the Y-cable is connected. This is because pin 20 is connected
between the
COMPUTER
and
TERMINAL
connectors, but not to the
PLOTTER
connector. ■
3
2
7
1
16
14
r ^
|
COMPUTER 3
1
2
7
PLOTTER
i
K^
'
TERMINAL
1
3
1
>
2 1 7
4
>
1
5
4
6
5
8
6 8
25
- i - ,
25
PINS 4, 5, 6, AND 8 THROUGH 25 ARE DIRECTLY CONNECTED BETWEEN THE
COMPUTER AND TERMINAL CONNECTORS.
Y-cable Schematic
RS-232-C/CCITT V.24 INTERFACING 10-11