Boot rom chip select!!

for a

It depends on the specific processor.

Pretty often it's the chip select corresponding to the startup address of the processor. In processors with programmable chip-select units it's the only chip select alive at reset. The idea is to put a fixed memory (e.g. Flash) with suitable code behind the boot chip select, so the chip select unit can be set up at startup.

For examples, get e.g. data sheets for Intel 80186 and Atmel AT91x4xx.

HTH

Tauno Voipio tauno voipio @ iki fi

This is based on Motorola's scheme as used in the 68HC16 and 683xx CPUs. The boot CS is available at device reset, read-only, of a fixed size and timed for slow memory, like EPROM. The memory-width (8 or 16 bits) is selected by pulling a data-line (#?) low during reset. After start-up, the chip-select's timing, address-range and width can all be changed by software. Wade Hassler