booting from expansion card

andyS91

Hi All,
i've got a question about booting from the EEPROM on a expansion card.
According to the 1. Chapter of the Hydra book programms can be loaded either from the on-board EEPROM or the EEPROM on the expansion card.
How does the hydra know if theres·cartridge in the port and how can it boot from the 2. EEPROM even though it's not connected to P28/P29?
Is it done in hardware or software?
I guess it's all explained in the book but since i don't own a hydra (yet? [noparse];)[/noparse] i could only read the 1. chapter.
By the way - is there a possibility to get·the hydra schematics without the book?
Thank you!
Andy

Mike Green

1) There's hardware on the Hydra that detects whether an expansion card is plugged in. If so, it changes the addressing of the Hydra's main-board EEPROM so that it responds to addresses in the range $20000-$3FFFF rather than the usual $00000-$1FFFF and the expansion card EEPROM then responds to $00000-$1FFFF.

2) There are a few small pieces of the Hydra Manual posted on the Parallax webstore page for the Hydra as you've noticed. You have to buy the Hydra Manual or the Hydra itself (which comes with the Manual) in order to get all the schematics and other information.

andyS91

Thank you Mike!
After reading you post I realized that I didn't know how adressing works with I2C.
Now i've got it.