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Didier Lachieze · (This post was last modified: 04-12-2018 03:35 AM by Didier Lachieze.)

Thanks for sharing !

There are some documents on TAS about the ERAMCO MLDL, and some pictures on Meindert's HP41 Museum.

Here is a review from the JPC n12 (March 1984), which was originally published along with another user evaluation in the PPC Journal - V11N1 Jan-Feb 1984:

Quote:ON THE ADVANTAGES OF USING AN ERAMCO SYSTEMS MLDL-BOX

Although most of the issues that will be covered by this article are common knowledge amongst MLDL users, specially ERAMCO Systems ESMLDL1 users, there are still enough readers of this magazine that have not even heard of an MLDL box, let alone know the differences and advantages of one or another MLDL-box. This article is intended to give a better view on the ERAMCO Systems ESMLDL1 MLDL-box without trying to give an opinion on other MLDL-boxes.

HARDWARE OVERVIEW

To give a view on the ESMLDL1 I will first review the hardware before turning to the included software. The hardware consists of a box measuring 6.25" * 3.25" * 2.0" (160 * 80 * 54 mm) with a plug to the HP-41 on a flat cable of approx. 6" (15 cm) length. The box is made of PVC and has cutouts for the cable and for the switches that are used to en/dis-able the RAM pages and to select the RAM page address.

Internaly you will find three printed circuit boards each filled to maximum with integrated circuits and a few discrete components. One printed circuit board is reserved for the placement of 12 EPROMS forming, together 24K Bytes of MLDL Eprom space. Each two (2) Eproms form one 4K page and can be en/dis-abled independently of the other Eproms on this board. Eproms have a fixed address in the HP-41 addressing space, occupying almost all available pages in the port addressing space. This results in the use of all ports except for a part of port 4, which remains free for use by the Card reader and a part of port 2 which could be used for a 4K application module.
The second board in this box is used to connect everything together and to connect the box to the HP-41. This is the controller board of the system containing timing and read/write logic for the ESMLDL1. Lots can be said on how to interface a MLDL to the outside world and to the HP-41, let it suffice to say here that the electronics of this board are well designed and able to cope with most HP-41's around. Machines running at more than 2x might suffer some problems due to the reduced load capability of the HP-41 circuits at those speeds. No other problems have been found until now.
The third board is the RAM board of the ESMLDL1 box and is the most interesting part of an MLDL box. This board contains 8K bytes of continuous memory (as long as the back-up battery is not empty) segmented in two blocks of 4K each. Each of these blocks can be placed independently of the other on a 4K address boundry. The en/dis-abling of one page is also independent of the other page and independent of the Eprom pages as long as no two pages share the same addressing space while being enabled. (Two or more pages can reside in the same address space but a maximum of one page can be enabled in this address space). An interesting feature of this RAM card is that it uses standard components and readily available parts to minimize cost and realize an 8K*10 bit memory space.

Memory retention is warranted through the use of a lithium battery that retains the memory contents for approx. 5 months, depending on how often the box is left connected to the HP-41. No current will be drawn from this battery as long as the box is connected to the HP-41. So the longer you leave the box connected to your system, the longer your battery will last.

Here also lays one weak point of the ESMLDL1: to replace the battery you will need a soldering iron as the battery is soldered into place. It is not a large operation however. Ask a friend if you are inexperienced with soldering irons. The battery is a standard Radio Shack part and should be available in most countries of the world. You might even consider to replace this battery with two used HP-41 batteries giving 3 volts together. It works and is a nice way to get most out of the hardware you have to buy for your system.

SOFTWARE OVERVIEW

A MLDL box without software is like a car without petrol. You can look at it, you can clean it and show it but you can do nothing useful with it. To an MLDL box applies the same. Without an operating system of some kind you will not be able to write into the memory of your box.This compared to a Protocoder is a disadvantage. The speed and ease of data entry using the included operating system Eprom try to makeup for this disadvantage. As the ESMLDL1 box is designed to conform to the existing standards in MLDL world all software written for other MLDL boxes will run on the ESMLDL1. The one exception is the software that uses the memory write properties of the ProtoCoder system. All other software, including the software of ProtoCoder systems, will run on the ESMLDL1.

The included software consists of three types of routines. The first type of routines cover all the actions that modify the memory contents of the ESMLDL1 box. These routines are a general read/modify/write routine, a routine to copy programs to MLDL memory area (the counterpart of COPY in the HP-41) a move utility and routines to clear the MLDL RAM, to save the contents of this RAM and various other utilities changing the contents of the RAM.
The second type of routines simplifies the access of the MLDL RAM without modifying anything in this area. Included functions are a function to locate a specified word in the MLDL RAM, to find the last used word in this RAM, to check memory contents for alterations (memory checksum). Also included in this section of routines is a Compile routine that calculates all XEQ's and GTO's, changing the GTO shape from two to three bytes if needed. Of course a COD and a DECOD function (NH and HN) are included to code and decode non normalized numbers. To even further enhance the use of this MLDL, routines to disassemble hex codes into instruction mnemonics are included, as well as routines to count the length of a program in bytes, to perform a selective catalog of user ports (CAT 2 starting at a specified ROM address) and a few functions to be used while writing synthetic instructions.
The third type of routines are USER-Code routines utilizing a few of the routines described above to disassemble a block of code, to store 4K of RAM on cassette and to retrieve a 4K block from cassette.

GENERAL COMMENTS

All in all this box presents one of the best values for money you can get in MLDL land now-a-days. The drawbacks are the high initial investment for those persons who only want to experiment a little with MLDL boxes, the size (twice as thick as a HP-41 and slightly longer) and the battery replacement. (See comment in hardware section.)

The main positive points are the page addressability of the RAM section the en/dis-abling scheme of Eproms and RAM and the use of the standard 040 write NOP. Another major positive point is, the use of separate Eproms for each 4K block. The box is FCC approved as is requested for computer equipment. Warranty is 180 days worldwide on materials and workmanship for the hardware as well as for the Eprom set (4K) that comes with the box.

ERAMCO Systems has been in the MLDL and Eprom market for almost one year and a half and has proven to be a company with products worth using. Service of boxes in hardware sense, repairs and requested updates are handled in a neat way, software in various fields is available and can be delivered with the box on request. (not free of charge)