Epson PX-8 Technical Manual page 128

REV.-A
The AUX signal is supplied to pin 4 of IC 12D and pin 8 of the IC 3E. When this signal goes low,
the two AND gates are disabled and the RS-232C interface is diactivated. And input/output
from/to the option unit is possible. When the AUX signal goes high, the RS-232C interface is en-
abled and the option unit is deactivated.
2.11.2.4 Operation Timing
Handshaking of this interface varies depending on software specification. Fig. 2-107 illustrates
the timing relationship among the interface operation signals.
SWRS
±8V
INHRS
DTR
Transmitter
DSR
RTS
CTS'
Data
fl
(space/mark)
Carrier
Receiver CD
Fig. 2-107 RS-232C Interface Signal Timing Relationship
<
Setting up for Communications>
The interface set-up operations are common to RS-232C transmitting and receiving. The SWRS
signal from GAH40M first enables the
±
8V regulator. At the same time, the INHRS signal is
activated to prevent the regulator output from being supplied until it rises beyond a certain level
and becomes stable. Then, the interface issues the DTR signal to check whether the connected
modem is ready. If ready, the modem responds to DTR with the DSR signal and waits for the
arrival of the RTS signal or carrier (CD). In the following discussions, either RS-232C interface can
be transmitter or receiver.
2-104