| ??? 10/24/07 16:56 Read: times |
#146145 - . Responding to: ???'s previous message |
Make sure you use at least a 32KB ROM a) "at least" is ridiculous, the "A15 trick" requires no more than 32k of ROM actually it is not very ridiculous. If you have a ROM carrying less than 32KB, and you have no code that causes a jump to a high address, then the system will eventually attempt to read address 7FFFh and at that address, there is nothing. This means that you could have unpredictable results. If you must use less than 32KB of ROM, make sure there is a JMP 8000h (or equivalent) instruction stored in your ROM, assuming 8000h is the starting location of RAM. If you have more than 32KB of ROM, it is ok. You could tie the remaining address lines to a latch and make a program in the first 32K of the ROM that controls the output of that latch, so that you can have more than 32KB of ROM space. Or, you can just tie those address lines to whatever values you want. Grounding the remaining address lines is OK. If your ROM is a FLASH ROM, then I think reading from it is no different. so it is NOT wrong to use 32KB ROM and up. |
