ENCAD CADJET, Service Manual

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2-8 Theory of Operation
CadJet 3D Service Manual
The system firmware is stored in Flash EEPROM. The Flash
EEPROM allows the firmware to be upgraded by downloading the files
containing the new firmware. It can be erased and reprogrammed more
than 10,000 times. The term “Flash” means that bytes cannot be
individually erased. A block or the whole device is erased at the same
time and the block or whole device is then reprogrammed.
The normal method of downloading new firmware is to send the unit the
files containing the code using either the GO.EXE utility or printing the
file to the unit. This requires using an appropriate host utility and can
be done through the serial port (for Macintosh users) or the parallel port
(for PC users). See Firmware Downloading in Chapter 3 for the proce-
dures.
DRAM
DRAM is Dynamic Random Access Memory which provides temporary
storage of the microprocessor calculation and input/output data. It is
also a faster type of memory then the Flash EEPROM. That’s why the
printer control program is also copied from the Flash EEPROM to RAM,
where it can be executed faster.
The printer also has two 72-pin 32-bit SIMM sockets for DRAM. The
printer is supplied with two 32 Megabyte SIMMs installed on the MPCB
for a total of 64 MB. The following SIMM sizes are supported: 32MB
(8Mx32) and 64MB (16Mx32.)
The SIMMs must have a minimum operating speed of 70ns, and
conform to JEDEC Standard 21-D release 4 or later. Remove the Right
Cover to install additional memory (see Chapter 5 for installation
procedures.) Care must be taken when choosing a SIMM module for the
printer. Not all SIMM’s on the market today will work on the printer.
It has to do with the “presence detect” signals on pins 67 and 68 of the
SIMM’s. Not all SIMM manufacturers use these signals, so they
disable them. Recommended SIMM’s to be used are listed on ENCAD’s
website.