I got this fine computer from Lino Lampers. Thanks Lino!
|Top||The PX-4, introduced in 1985, is successor of the by then aging
HX-20 (from 1981),
but is based on the PX-8. The HX-20 was positioned as a portable terminal
to be used in the field, the PX-8 was more geared for administrative
uses on the road. The PX-4 is similar to the the PX-8 on the outside,
but included features from the HX-20 like modular peripherials as
printers, mini-cassette and extra RAM. As the internal architecture
is quite different, most hardware related PX-8 programs do not work
and vice versa (like FILINK.COM or CONFIG.COM). It runs generic CP/M
programs and has a virtual 80x25 (configurable even to 80x50!). The
actual screen is 40x8.
The PX-4 was followed by the PX-4+, which at least incorporated the 120 kByte RAM disk.
|The PX-4, being slightly newer than the PX-8, contained some
features not found on the older model.
The PX-4 at the left has an "Item keyboard" installed. Here is a hi-res scan of the overlay.
|Family||Following the PX-4 Epson developed the PX-16, a portable PC compatible which by its modular construction could be used as field terminal (compact, sturdy & lots of options) or as portable (PC compatible complete with 80x25 monochrome LCD screen). In fact, the PX-16 is a recreation of the PX-4, but PC-XT compatible. The cartridge interface of the PX-4 and PX-16 is the same.|
|PX-4 PINE board||The PX-4 (Pine) board is less populated than the PX-8 (Maple) board.
The 6301 additional processor and the discrete 82C51 USART are gone.
Epson probably realized a slow 6301 didn't add much functionality
next to a 3.6 MHz Z80.
This may be the main reason of the reduced power consumption.
The disadvantage of having the Z80 processor suppory all functionality, is that about 10 kByte less is available for the TPA (and RAM disk):
A weak spot is the backup batttery, an Epson RB 301 4.8V/90mA NiCd back. The dimensions are 67.7 mm long, 14.4 mm diameter. 1/4AAA NiMh 1.2V, 80mA (11 mm long, 10 mm diameter) are still for sale and could be used to construct a replacement with 4 cells in series. The PX-4 will work without, but will not keep memory when switched off (same as backup switch off).
|RAM disk board||The External RAM Disk board is not "Intelligent" as the PX8 type was.
No Z80 and ROM, but still dynamic RAM. There is a rechargable battery
The ROM capsule socket is upward compatible with the internal ones, but larger sizes are not supported by the operating system. It appears as drive J:. User programs can access the larger than 32 kByte capacities, assuming you find the correct chips or equivalent (128 kByte masked PROMs existed in 28 pin packages). ROM capsule switches:
|PX-4+ PINE II
|The PX-4+ is an upgrade of the PX-4. Both the 120 kByte RAM disk and
the extra ROM socket is integrated. The extra socket maps to drive J:.
Some related jumpers:
Between the battery compartment and cartridge-bay two connectors suggest an interesting, but unknown option. There is also a socket for a permanent OS ROM extension ROM.
Latest update: 2022-06-18