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MAVRIC-II-REMAVRIC-II 128K RAM Expansion
FEATURES: • 128K external static RAM for MAVRIC-IIB and MAVRIC-II • Small size at 1.8 x 2.2 inches NOTE: Not RoHS compliant The MAVRIC-II-RE provides 128KB of external static RAM for your MAVRIC-IIB or MAVRIC-II microcontroller board. The MAVRIC-II board includes 4K of internal static RAM by way of the ATmega128 chip. While 4K is considered large for a microcontroller, some applications are more demanding in terms of memory. What do you do when you find you need more than 4K? It's hard to just switch controllers because you won't find very many with more RAM than that. Usually, the only alternative is to switch to a 16 or 32 bit SBC (single board computer) which are much more power hungry and a lot more expensive, and that also means a total rewrite of your application. But with the MAVRIC-II-RE daughter card, you can instantly upgrade
your MAVRIC-II, expanding its memory capacity to 128K. Note that
the ATmega128 can only directly address the lower 64K, however,
we've provided the ability for you to optionally jumper PD5 to the
A16 address line so that you can access the whole 128K via bank
switching.
What ports does the memory expansion bus consume? In an ideal world you would be able to fully utilize all the ATmega128 port pins and address external memory using the external memory bus simultaneously. However, the nature of the ATmega128's external memory bus requires the use of PORTA, PORTC, and 3 pins of PORTG - PG0, PG1, and PG2. If you make use of the upper 64K via bank switching, utilizing all 128K of RAM, you must also use 1 pin of PORTD, PD5. Thus, the external memory expansion comes at the cost of 19 or 20 I/O lines. But the ATmega128 is a powerhouse of I/O and peripherals, so the remaining 32 or so I/O lines still pack quite a punch with regard to control. Note that the address and data bus pins required for the external memory are not shared with any special on-board perhipherals, so you won't be giving up any ATmega128 special features.
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