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AM2545 Module - Eµ Memory
Overview This module is a clone of the Memory module in the Eµ Systems Modular Sequencer. It is a very close replica with only minor changes to use modern components and to add some
new features. The 2545 is a 512 step volatile memory for holding 8-bits of data. This data is separated into 6-bits for a control voltage and 2-bits for 4 digital ON/OFF signals.
The data is programmed into the memory by the 2546
Programmer Module, and addressed by the 2540 MAG module. The control voltage data is available both as a standard 1V/Octave and as a preset voltage scale, which can be internally set or controlled by a front panel control. The digital data
is decoded such that only one of the 4 signals is ON (high) at any step.
The MAG creates a 9-bit binary code for addressing the 2545; this enables 512 steps to be stored. The 2545 clone has 16x more memory than the original. To
address this additional memory, a 2541 Bank Address Generator can be used to send 4-bits of data to select 16x banks.
Original Circuit
The original design dates back to late 1973, and I have cloned the original schematic and added some new features. The core of the circuit was a bank of four 2101 1k bit SRAM chips that stored the data. However the memory is volatile with no battery backup, Dave Rossum created the 2547 Tape module so the data could be backed up.
The 8 bits of data is sent to a 6-bit DAC based on a resistor network. The 2 bits of digital data is decoded with some CMOS chips, which are buffered with transistors to create the outputs and to drive the LED's.
The 2101's are organised as 256 x 4 bits. They are addressed from 9-bits; 8-bits drive
A0-A7, and the ninth bit is addressed via the CE2 pin. The chips are switched from read to write by pin 20 R/W, when HIGH the data can be read.
Writing to the chips is only possible when both the front panel WRITE ENABLE switch is set ON and the 2546 Programmer delivers a LOW signal (WE) to the 2545.
AM Circuit
The AM circuit is exactly the same except that the obsolete 2101 memory has been replaced with one modern 16k SRAM chip with onboard lithium battery to provide memory storage after power down. The battery lasts 10 years. This chip provides 16x the memory, enabling 16 separate banks of data to be held.
The Maxim DS1220 16k SRAM is organised slightly differently to the 2101's. The chip has 8-bits of data, which are addressed from 11-bits. To read data the chip needs WE HIGH and CE and OE LOW. To write data the chip needs WE and CE LOW and OE HIGH. An additional CMOS NAND gate has been used to provide a WE signal to the chip.
Upgrades:
- Non volatile RAM
- A modern parallel 12-bit DAC chip to provide a more accurate control voltage
- Emulator 2 style push buttons with latching circuits for WRITE ENABLE and PRESET/VARIABLE
- A revised voltage reference using a 0.6ppm precision voltage reference chip
- Blue and Red 5mm LED's
- Maybe ad note display on 7 segment LED?
The rest of the circuit is a direct clone. The 2 bits of digital data is decoded with some CMOS
chips, which are buffered with transistors to create the outputs and to drive the LED's.
The circuit has been laid out over 3 separate PCB's:
- A front panel board which holds the 2-bit decoder and drivers, plus buttons
- A Memory board which holds the SRAM chip and its connections.
- A DAC board with the DAC circuitry.
There is no trimming.The module needs +5V for the CMOS logic and SRAM chip.
Front
Panel The panel is a standard AM design, 90mm wide and 4U high, with black lettering. Controls knobs are the standard Eµ Modular design.
Build History
The schematic was transferred into Eagle CAD in the summer of 2005 when I was on holiday in the Peak District (UK). The circuit has been laid out over 2 80x100mm PCB's and a prototype will be tested in the Spring of 2006.
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