HP 7470A Interfacing And Programming Manual page 112

) oc
ex
)
T^
' d^
1
H
to|
)H
) »
a .
)
Additional Connector Pin Allocations
)
iS)
74,
er)
. i e
N
;^
7 ;
/ei}
W
e
ID
v s f
aCj
XT
P i n No.
1
4
17
RS-232-C CCITT V.24
20
AA
CA
DD
101
105
115
F u n c t i o n / S i g n a l Level
CD
14*
16*
SBA
SBB
108.2
Protective ground
Request To Send from the
plotter
Always High'= ON = "0"
s + l 2 V
External Clock Input
High = ON = +2.4 V to
+ 5 V
Low = OFF = 0.0 V to
+0.4 V
Data Terminal Ready to
modem
High = ON = "0"
2 + 1 2 V
Low = OFF = " 1 "
118
119
s - 1 2 V
Secondary Transmit Data
Data line from plotter to
terminal
Secondary Received Data
Data line to plotter from
terminal
' *Used to establish monitor mode with special Y-cable (Part No. 17455A).
P
ri
s;
ii
^Output Baud Rate
C1C
i<)-14
)
e ^
ise,
The plotter is designed to operate in an asynchronous mode with
switch-selectable baud rates of 75, 110, 150, 200, 300, 600, 1200, 2400,
4800, and 9600. See the 7470A Operator's Manual for instructions on
setting the baud rate. However, setting all
BAUD
switches to zero and
connecting an external clock input to pin 17 of the connector allows
operation of the plotter at any intermediate baud rate up to 9600 baud.
Both the receiver (RRC) and transmitter (TRC) clocks will operate at
the same clock rate. Requirements for the clock signal are as follows:
1. The clock frequency must be 16 times the desired baud rate.
2. The baud rate must not exceed 9600.
Tia) 3. The duty cycle of the clock pulse should be close to 50%.
10-12 RS-232-C/CCITT V.24 INTERFACING
4. The clock pulse must be a logic on of +2 V < V < 25 V and a logic off
of - 2 5 V < V < +0.8 V (3.5 k n input impedance).
5. Care should be taken to keep the transmission lines as short as
possible to minimize transmission line reflection noise.
Stop Bits
The plotter is configured to automatically verify or generate one or two
stop bits, depending on the setting of the plotter's baud rate switches.
Refer to the 7470A Operator's Manual for more information.
Transmission Errors
Transmission errors occur when communication between the computer
and plotter is incomplete or does not conform to what is expected or
required by either party.
Transmission errors include:
• Framing error — the plotter does not detect a valid stop bit at the end
of every character.
• Parity error — the plotter does not detect the expected parity (odd or
even).
• Overrun error — a plotter instruction writes over another instruction.
• Buffer overflow error — the plotter receives more bytes of data t h a n it
has space for in the buffer.
When the plotter detects a framing, parity, or overrun error, it turns on
the front panel ERROR light and sets error code 15. This error code
generally indicates that the communication incompatibility is hardware
related (incorrect stop bit jumper installation, wrong parity selection,
incompatible or incorrectly set baud rates, etc.).
When the plotter detects a buffer overflow, it turns on the front panel
ERROR
light and sets error code 16. The last HP-GL data t h a t caused the
overflow will be lost. Error code 16 generally indicates an improperly
established handshake protocol.
The
ERROR
light remains on until either the user interrogates the plotter
via an output extended error command, ESC . E, and the plotter re­
sponds with the appropriate error code, or the user turns the plotter off,
or an HP-GL initialization instruction, IN, is processed, or a front-panel
reset occurs.
A complete list of error codes is included with the discussion of the
E S C . E instruction.
RS-232-C/CCITT V.24 INTERFACING 10-13