Heathkit H14 Manual page 11

Page 9
~I--_-------------
•
MAX. OPEN-CIRCUIT
ORIVER VOLTAGE
MAX. OPEN-CIRCUH
TERMINATlll VOLTAGE
MIN. OPEN~CIRCUIT
TERMINATOR VOLTAGE
( +251
1+21
1-2)
} SPACEloN
}TRANSITION UNDEfiNED
}MA"IOfF
•
MIN.OPEN-CIRCUIT
ORIVER VOLTAGE
, -251
PICfORIAL 2
•
All control signals are at RS-232C levels. (See Picto-
rial 2.) All controls are "on" in the space condition
(binary 0). All I/O signals are at "mark" during all
intervals between valid data transfers.
PRINTER HANDSHAKING
Requestt. Send (RTS)
RTS (Pin 4) may be used. as a printer busy signal. This
allows data to be transmitted at baud rates greater
than 110 without a chance of losing characters. and
still allows the system to operate at its maximum rate.
When the Printer's line buffer is full, the RTS line
goes to the "on" state and will remain there until the
buffer can accept more characters. When RTS goes
"on," there is room for sixteen more characters in the
buffer.
An additional handshake signal is generated in the
form of control
Q
and control S, which is transmitted
on the regular data output channel. When the line
buffer is full. the RTS output goes to the "on" state
and the control S signal will be sent. When more data
can be accepted, the Printer will send "Control
Q"
and the RTS will go "off."
NatE:
If the Printer stops unexpectedly, restart by
using the "Off Line" swtich. No characters will be
missed.
Data Terminal Ready (DTR)
The DTRsignal is "on" whenever the AC power is on.
PRINTER BAUD RATE AND SIGNAL LEVELS
SELECTION
Refer to "Printer Baud Rate Selection" and "Printer
Signal Levels Selection" on Page 6.