HX20 <--> Linux PC   SERIAL LINK
             ------------------------------------



Wiring Diagram
--------------
Connectors: Epson HX20 has DIN 8-pin (TCS4480) connector (female).
            Watch out, there are two versions, you need the one with the two
            upper pins (6, 7) closer together and to the middle (8).

            PC uses standard DB 9 and DB 25 male serial connectors (V42).

            The cable is wired as NULL-MODEM cable with criss-crossed
            handshake and data lines.



DIN 8-pin (female):                    Pinout:

              .---.   .---.            1    GND
            ./    |   |    \.          2    TXD
           /      \___/      \         3    RXD
          /                   \        4    RTS
         |    *7          *6   |       5    CTS
         |          *8         |       6    DSR
         |   *3            *1  |       7    DTR
         |                     |       8    CD
          \     *5      *4    /        case protective ground
    	   \.       *2      ./
             \.           ./
               \_________/


Signal:              PC:                          Epson HX20:
(seen by PC)         DB 25     DB 9               DIN 8-pin
---------------------------------------------------------------
signal ground        7         5                  1
RXD                  3         2                  2
TXD                  2         3                  3
CTS                  5         8                  4
RTS                  4         7                  5
DTR                  20        4                  6,8
DSR                  6,8       6,1                7
protective ground    1                            case

(Carrier Detect      8         1                  8)
(CD is routed to each DTE's DSR signal to simplify programming.)


Testing the link
----------------
On your Linux machine, you might do:
	stty 4800 -parity cstopb crtscts </dev/ttyS0
	cat /dev/ttyS0
which will display the incoming characters.


On the HX20 you might do:
	LIST "COM0:"
which will send the current BASIC program to the PC.


Due to power-saving hardware, the Epson's serial port does not start
up cleanly, but throws out one first character that looks like
0xf3. This can be avoided by an early OPEN.


File Transfer
-------------
For *ASCII* file transfer, you need to add "opost onlcr" to the stty parameter
list. This will translate the Linux-style linefeed to NL-CR
(\n\r). For the reverse, setting "igncr" strips the CR character. If
you transmit files, it's safer to use a low speed, otherwise the
HX20's unreliable buffering gives out. I use the following script:

--------------------script-----------------------
# !/bin/sh
#
# Slow Epson HX20 Text Transfer
#
stty 600 -parity -cstopb crtscts igncr opost onlcr </dev/ttyS0
echo 'On HX20, type: LOAD "COM0:(38N13)"'
echo 'Here, cat to /dev/ttyS0'
-------------------------------------------------

You can save a program from HX20 to Linux by using:
        cp /dev/ttyS0 program.bas
and on the Epson HX20:
        SAVE "COM0:(38N13)",A
This direction works also faster.


For *Binary* file transfer, you want a raw serial line, such as does
this:

--------------------script-----------------------
# !/bin/sh
#
# Fast Epson HX20 Binary Transfer
#
stty 4800 -parity -cstopb crtscts -igncr -opost </dev/ttyS0
echo 'On HX20, use "COM0:(68N13)"'
-------------------------------------------------

Remember that when transferring data by means of a BASIC program, the
PRINT #1, CHR$(byte) command is limited by the buffer size. Default is
80 Bytes (printer width), using WIDTH "COM0:", 255 gets you the
max. PRINT then puts out a 0x0d 0x0a linefeed sequence.

Special Characters from the ISO-8859-1 set can not be treated
correctly by the serial drivers. Maybe "recode" has help for this. The
Epson maps specific national characters to @{|}[\], as do old printers.


Author
------
Martin Woelz      eMail: woelz@web.de