Design Ideas: January 4, 1996
The design in Figure 1 allows for a single board to support both an 8- and a 16-bit bus width. The 8-bit Am186EM µC would use both SRAMs and have 0 Ohm resistors or jumpers connecting A17 and WHB to the SRAMs. The 16-bit Am188EM µC would use a single SRAM and have 0 Ohm resistors or jumpers connecting A0 to the SRAM and WHB to ground. A high or low level on the BYTE input of the Am29F200 flash memory configures the device as either 256k×8 or 128k×16 bits, respectively, as the figure shows.
A 40-MHz Am186EM µC would provide 5.35 VAX MIPS (Visual C++ v.1.52) using 70-nsec memories. The 40-MHz Am188EM µC would provide approximately 3.38 VAX MIPS using the same 70-nsec memories. You can achieve even more performance and price variation by reducing the frequency of the µC. Both the Am186EM and Am188EM µCs are available in 20-, 25-, 33-, and 40-MHz frequencies. This flexibility allows for performance variation from the hardware without changing the software. The 8-bit version would save in the cost of the µC and the memories. (DI #1805)