The Epson HX-20, PX-8 and PX-4 are all equipped with two ports, one labeled "SERIAL" the other labeled "RS-232C". On most other computer devices these terms are synonymous, but not for these Epson portables.
The information here is extracted from the HX-20 Technical Manual hardware, the PX-8 User manual and the PX-4 Operating Manual, which can all be found on this site.
For the HX-20, the SERIAL port is the interconnection between the 6301 main and 6301 slave CPUs. It usually operates at 38400 Baud and is intended for the external Display Controller and Terminal Floppy drives (TF-10, TF-15, TF-20). In this case, the protocol here is epsp. The SERIAL port can also be used with an 4800 Bd serial printer.
The RS-232C port on the HX-20 is controlled by the 6301 slave CPU and intended for communication with another computer, either directly or via a modem, like the CX-20 acoustic modem.
For the PX-8, SERIAL port is controlled by the 6301 slave CPU and intended for Terminal Floppy drives (TF-10, TF-15, TF-20, PF-10). In this case, the protocol here is epsp. The SERIAL port can also be used with a 4800 Bd serial printer if the port is selected through the CONFIG printer I/F setting. Tyical cables are #723 (TF-10, TF-15, TF-20), #726 (PF-10), #725 (printer).
The RS-232C port is attached to a 82C51 UART on the system bus and intended for communication with another computer, either directly or via a modem, like the CX-20 acoustic modem. The RS-232C port can also be used with a 4800 Bd serial printer if the port is selected through the CONFIG printer I/F setting. Typical cables are the #724, #725, #726.
On the PX-4, there is no 6301 slave CPU and all serial interfaces are handled through a single Serial controller. The serial interfaces are the SERIAL port, the RS-232C port and the cartridge port. The cartridges that make use of the cartridge port are the RAM cartridge, ROM cartridge, Micro cassette deck, Multimeter unit, Universal cartridge, Cartridge printer.
The cables used are the same as used with the PX-8; #723 to #726.
| number | description | reference |
|---|---|---|
| #705 | HX-20 to a PC DB25 connector (Japan only) | HX-20 tmH_TOC-01-02:TM_02_0019 |
| #706 | HC/HX-20 to CX-20 acoustic coupler cable (USA only) DIN 8-pin - Canon 25-pin (Y201306000) | HX-20 tmH_TOC-01-02:TM_02_0019 |
| #707 | HX-20 to Display Controller and Display Controller to TF-10/15/20 cable. DIN 5-pin - DIN 6-pin (Y201307000) | HX-20 tmH_TOC-01-02:TM_02_0020 |
| #714 | HC-20 to printer cable (Japan only) DIN 8-pin - Canon 25-pin (Y201309000) | HX-20 tmH_TOC-01-02:TM_02_0022 |
| #715 | HX-20 to printer cable (USA only) DIN 8-pin - Canon 25-pin (Y201310000) | HX-20 tmH_TOC-01-02:TM_02_0022 |
| #716 | HC/HX-20 to HC/HX-20 cable DIN 8-pin - DIN 8-pin (Y201311000) | HX-20 tmH_TOC-01-02:TM_02_0023 |
| #717 | HC/HX-20 to HC/HX-20 cable DIN 5-pin - DIN 5-pin (Y201312000) | HX-20 tmH_TOC-01-02:TM_02_0023 |
| #723 | PX-4/8 - TF-10/15/20 | PX-8 um4:um4_30-31 |
| #724 | PX-8 to a modem or acoustic coupler with a DB25 connector | PX-8 um4:um4_26-27 |
| #725 | PX-8 to a computer (or printer) which is equipped with an RS-232C interface and a DB25 connector | PX-8 um4:um4_26-27 |
| #726 | two PX-8s or PX-4s through the RS-232C interfaces (PX-8 UM) or PF-10 micro floppy drive | PX-8 um4:um4_28-29 |
| #738 | PX-4/PX-8 to HC/HX-20 null modem cable | PX-8 OSRM |