Epson PX-8 - Page 129

REV.-A
< Transmission>
The transmitter interface issues the Request to Send (RTS) signal to its modem. This causes the
modem to output a carrier over the communications line to put the receiver RS-232C interface in
the receive state. After this, the modem returns the Clear to Send (CTS) signal to the transmitter
interface. This causes the interface to initiate a serial data transmission. The modem modulates
and transmits the data bits over the communications line.
< Reception>
The carrier, arriving over the communications line, is detected in the receiver modem after passing
through a hand-pass filter. This state is informed to the receiver interface via the Carrier Detect
(CD) signal. The interface assumes the Ready-to-Receiver state and the subsequently arriving data
is
demodulated by the modem and is read by the receiver interface. Fig. 2-108 illustrates the sig-
nal
follow, including flow over the communications line.
DTR ...
1
RDy
h
....
Transmit
.... DSR
I
___ -I
....
side
RTS
OSC
-
.... CTS
,
J
Communications line
TXD
-
r-
-
t--
....
~
c
0
~
....
~
::::l
I
'0
I
0
I :'2:
) Transmitter modulator/
/ demodulator (modem)
RS-232C levels
,.4
-
P""
-
Fig. 2-108
2-105
dRDY~
fE-D~
Receive
DSR
....
side
L _____
,
c
RTS
.Q
r------
....
~
CTS
::::l
r------
'0
0
E
CD ...
r-
Ql
"'"
t--
0
....
RXT ....
- ,
~
I
\
Receiver modulator/ ~
demodulator (modem) \
RS-232 levels