ok, First check this jumper configuration
Epson LX800 and the 390
Application : Epson LX800
Vendor : Epson
Platform : Serial Printer
Version : NA
Notes : Select "Epson" Presets in I/O configuration menu. Ensure that both the serial DIP switches and the mode DIP switches are set properly on the printer. Set jumper J8B on the serial interface board to Off (disconnected). This has the effect of disabling XON/XOFF flow control.
Epson I/O Presets
Baud = 9600
Pin5 = CTS
Format = NEW
rci = off
Dec.Pt. = ON
CR = CRLF
comp = off
Xmit = Manual
Width = Full
Serial DIP Switches - Epson LX800, LX810
Switch Bank #1 Switch Bank #2
Number Description Number Description
1 OFF 8 Bit Word 1 ON Serial I/O Enable
2 OFF No Parity 2 ON Buffer Enable
3 OFF 3 OFF Buffer FIFO Control
4 OFF 4 OFF
5 OFF 9600 Baud 5 OFF Self Test Mode
6 ON 6 OFF
7 OFF
8 OFF
Mode DIP Switches - LX800
Switch Bank #1 Switch Bank #2
Number Description Number Description
1 OFF Normal characters 1 OFF 11 inch paper
2 OFF Unlashed zero 2 OFF Tractor feed
3 OFF Italic character table 3 OFF No Skip over Perf
4 OFF Paper-out detection 4 OFF NO auto CR/LF
5 OFF Print quality = draft
6 ON USA character set
7 ON
8 ON
Second try to disable XON/XOFF flow control. and check the cable to ensure that only TX, RX & GND are present
and third as last resort you should emulate the centronics handshake with the pic. this is not hard, but I dont know how is the behaivor of the signals. last month I tryed to use the parallel port in EPP mode , I configure the bios, and w98 & dos recognize the port in that mode. but due to certains incompatibilitys of that specific chipset i cant use the port.
once again I dont know behaivor of the signals, maybe you should see with an osciloscope, and emulate the signals with the pic, but i think the signal and timmings may change with the driver in use.
check this link
http://HTTP://WWW.BEYONDLOGIC.ORG there is a lot of information about the ports.