Yet another computer museum
The Epson PX-4 cartridges

One of the most apparent features of the PX-4 was the cartridge bay. Apart from developing several cartridges themselves, Epson also provided full documentation on the cartridge interface, so third parties could make cartridges too. Below is an overview of the cartridges developed by Epson.

Epson Px-4 ROM cartridge The ROM cartridge is fully supported by the PX-4 OS and maps the ROMs default as J: and K:. The ROM types supported are the same as for the internal ROM drives (B: and C:), 8kByte, 16kByte and 32kByte.
As these ROMs are I/O-mapped, unlike the B: and C: ROM, P-type ROMs like BASIC will not work. (Source: Oprating Manual 1.2.6 ROM capsules)
RAM Epson Px-4 RAM cartridge The RAM cartridge is fully supported by the PX-4 OS and maps the RAM as disk I:. The standard Epson RAM cartridge contains only 16 kByte, but 32 kByte and 64 kByte are supported too. The third party cartridge shown here contains 128 kByte. Without driver, it reports 32 kByte in size.

Kit Bullough send me this info on the cartridge:

Epson UK were unhappy that the literature said a 64K was available but Epson NEVER made one bigger than 32K so asked me to manufacturer 64K units - I decided to also make and sell 128, and 512 units packed in the same cartridge. At the time only a few governments and airlines could afford that "world's biggest" state of the art memory pack and I hand to have an export licence from the UK government as it was considered "of military importance" - The United States invasion of Grenada 1983 had used a laptop with less memory on the invasion beach.

Epson had to use the mass production system and the time to get a larger cartridge would have taken a year or 2 to get ready - I made the larger cartridges using the latest components and in smaller quantities for governments and other organizations that needed the extra memory immediately. I also transferred to the Px-16 when it was available.

A batch of about 50 PX4 portables was sold to the Nederland Central Bureau of Statistics each with a ram pack designed and manufactured by me. The original idea was for the gathering of employment statistics by taking a laptop to peoples door. The larger memory capacity was considered necessary at the time but not available from the laptop manufacturers.

A special 128 kByte cartridge was designed as a sealed unit and has a U.S. military grade lithium battery developed from a heart pacemaker battery with a theoretical life (based on the drain on the battery) of over 50 years. Some buyers were uncomfortable with the idea of not changing a battery although today we are quite happy with a micro XD card.

The data bus was multiplexed using 4 unused lines to expand the capacity by a maximum of 32 times in the largest we made. As the cartridge was only used for dedicated applications the driver software was supplied to the end user and incorporated into the application software.

Epson Px-4 Microcassette Drive The microcassette drive is fully supported by the PX-4 OS and maps to drive H:. The "FREE" LED indicates the tape may be removed from the drive. The "REC" LED indicates data is being written to the tape (Source: Operating Manual, 4.1.3 Microcasette drive).
Epson Px-4 Cartridge Printer The Cartridge Printer is fully supported by the PX-4 OS. The width is 60 dots or 40 characters. A character is printed as 6 x 8 dots. The ribbon cartridge is ERC-09 B.
The active printer is selected with DIP switch 5 and 6 (Source: Operating manual, 4.3 Printers);
Switch 5Switch 6Interface
OFFOFFSerial interface
OFFONRS-232C interface
ONOFFCartridge printer
ONONParallel printer
Modem Epson Px-4 Modem cartridge The modem cartridge is not supported by the PX-4 OS, so needs special software to function. It can dial and auto anwser and communicate up to 300 bps (Bell 103). The internal PX-4 RS-232 port is used for data transfer.
In the Operating System Reference Manual is a Modem Sample Program that demonstrates the cartridge. As I have no modem cartridge, I cannot test this.
Digital Multimeter Cartridge
Epson Px-4 DMM cartridge The DMM cartridge is not supported by the PX-4 OS, but needs additional software to function. The ranges are:
  • DCV: auto, 300mV, 3V, 30V, 300V, 500V
  • ACV: auto, 3V, 30V, 300V, 350V
  • Ohm: auto, 300ohm, 3kohm, 30kohm, 300kohm, 3000kohm
  • Low power ohm: auto, 3kohm, 30kohm, 300kohm, 3000kohm
The DMM is powered by its own two AAA-type batteries.
The DMM cartridge operates in IO mode and communicates over a serial line with the CPU. 600 bps, 8-bit, no parity, one stop bit (Source: Operating System Reference Manual, DMM cartridge).
The serial line is the third serial option, next to the RS-232C and SERIAL (SIO) options. As all share the same UART, they cannot be used simultaneously (Source: Operating System Reference Manual, 5.2 Serial Interfaces)
Epson Px-4 PROM WRITER cartridge The PROM Writer cartridge is not supported by the PX-4 OS, but needs special software. An example is the ROMWRITE capsule ROM. A description of the software is available. The PROM Writer supports 2764, 27128 and 27256 type EPROMs.
Another package in ROM is PROM WRITE 2, which is an integrated image creator and programmer. The manual is in the Virtual library.
Connectors Cartridge connectors, 2 x 15 pin. The cartridge connector, PX-4 side at the bottom, cartridge side at the top. The Operating System Reference Manual names it PICL-30S-LT from JAE, Japan Aviation Electronics.

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Latest update: 2022-09_06