The gnuCsimm Project
~~~~~~~~~~~~~~~~~~~~~
I am proposing an Open Source project to develop a free, 72 pin 68332
based microcontroller SIMM module. In early 1998 I started developing
a device, but other commitments got the better of me. The design I am
proposing is based on the assumption that the builder has the ability
to fabricate the board, assemble it and program the bare unit from
scratch.
This device is not a replacement for the uCsimm, but targets a
different
application: Data acquisition and embedded control. For example, the
LCD
interface is dropped and we gain a 16 channel Time Processig Unit, which
can measure frequency, period, pulse width, etc and generate frequency,
pulse, PWM, stepper control, etc.
The '332 does not have a Bootstrap Mode, however a small (8Kb or 32Kb)
boot EEPROM can be programmed from the BDM interface. In turn, it can
be used as the primary debugguing/FLASH programming interface.
The 72 pin footprint allows many more interface pins to be brought out
to the host board, the address/data bus, TPU pins, interrupts, SCI, SPI
and severel general IO pins. It also allows more hardware on the SIMM,
which is necessary as the '332 is not as standalone as the '328.
The '332 needs pullup/down on the address bus coming out of reset to
set boot options. It also has a maximum of 1Mb address space on each
Chip Select pin, so only chips of 1Mb or less address space can be used
without external circuitry. There is no Real Time Clock onboard, so an
external RTC is needed.
Fortunately, there are 9 Chip Select pins available, as well as a
dedicated CS for the boot ROM device. As a starting point, I would
suggest two 512Kbx16bit FLASH chips, four 512kbx16bit SRAM chips, CS8900
ethernet, and an 8bit RTC. This leaves one CS pin for external devices,
however, two of the SRAM CS pins will be available on the connector, so
if the chips are not installed, they can select off-board devices.
Also,
if the SRAM/FLASH chips are pin-comaptible, they can be interchaged for
a specific application.
If you are interested in this project, send me some email with a short
description of your experience with this chip. I'll create a mailing
list
and we can start discussing the peripherals and capabilities. After the
details are pinned down, we can move onto schematics and then the PCB.
Cheers, glen.
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