Rs-232C Interface - Epson PX-8 User Manual

4.2 RS-232C interface
The PX-8 is equipped with an RS-232C interface and the operating system sup-
ports a communication speed of up to 19200 bps. The RS-232C interface is used
to communicate with other computers, to modems acoustic couplers and printers
and other devices which support this communication standard.
The operation mode of the RS-232C interface can be specified with the CON-
FIG program in Chapter 3 or by using the OPEN command in BASIC.
The SHIFT-IN/SHIFT-OUT and
XON/XOFF
functions are also supported
by the operating system, but can only be set by BASIC.
The SHIFT-IN/SHIFT-OUT protocol allows the full ASCII code from 0 to
255 decimal, but only using seven bits.
It
only operates during seven bit trans-
mission. When a code greater than 127 is required, the SHIFT-OUT (SO) code
is sent to tell the receiving device to set the high bit, i.e. to add 128 to the code
received. Thus if the code 65 is sent when the SO has been sent the receiving
computer will interpret it as code 193 (65
+
128). The SHIFT-IN code reverses
an SO condition.
If
a code 193 is sent at when an SI code has been sent the
code will be interpreted as code 65. The SIISO codes act as a switch. For exam-
ple all characters will have the high bit set until the SI code is sent once an SO
code has been sent.
When communication occurs with two devices using
XON/XOFF
protocol, the
transmitting device can be told by the receiving device to wait until the receiv-
ing device is ready to handle further information. This is important if the receiv-
ing device is processing the information and needs time to carry out some
operations before receiving more data.
The codes for SIISO,
XON/XOFF
are:-
Decimal Hexadecimal
SO 14 0E
SI
15
0F
XON 17 11
XOFF 19
13
A warm boot will set the default setting of SIISO and
XON/XOFF
to off, and
thus to ensure they are not active, perform a warm boot before using the CON-
FIG program to set the parameters.
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NOTE:
The CONFIG program does not allow the XONIXOFF or SIISO protocol to
be set. This can only be done from BASIC, or a machine code BIOS call.
WARNING:
When sending data which could contain these characters for example a
machine code program, the SHIFT-INISHIFT-OUT and XONIXOFF
options should be set to off If this is not done, when the receiving device
is sent any of the above characters it will be interpreted as such and the
appropriate action will be taken. Consequently the data received will have
the bit setting ch9nged in the case of SIISO. Also the particular character
being sent as control data (SIISOIXONIXOFF) will not form part of
the data received as it will have been interpreted as a control character.
Before using TERM or FLUNK execute a warm boot to set the RS-232
parameters to the default, and then change them using the CONFIG program
if necessary. This ensures the SIISO and
XON/XOFF
parameters are set to off.
The RS-232C interface can also be used in BASIC programs. For details of use,
refer to the PX-8 BASIC Reference Manual.
The PX-8 uses the RS-232C interface to connect a printer unless the system
configuration is changed with the CONFIG command.
Examples
of
use
The following command transmits the contents of file SAMPLE. TXT to the
RS-232 interface.
PIP PUN:
=
A:SAMPLE.TXT
The following command receives data from the RS-232C interface and saves
it on the disk in drive A: under the file name SAMPLE2.DAT.
PIP A:SAMPLE2.DAT
=
RDR:
The default settings of the RS-232C interface operation mode are as follows.
Communication speed:
Character length:
Number of stop bits:
4800 bps
8 bits
2
Parity check:
SIISO control:
XON/XOFF
control:
4-23
No
No
No