| ??? 11/13/08 06:53 Read: times |
#160004 - PDATA & XDATA Responding to: ???'s previous message |
Richard Erlacher said:
Until they actually put a significant amount of xRAM on-chip, external will continue to have meaning beyond the historical. OK: what I meant was that taking the 'X' in XDATA to mean "external" is now meaningless, since many chips have internal XDATA - and some support both internal & external XDATA. I think some people use "EDATA" to indicate internal XDATA? I'd guess that 64KB of SRAM would do, for starters, but it would have to have external access as well as internal, since not everything happens on chip. Yes: my point was meant to be that its classification as "XDATA" is purely to do with how it's addressed, and nothing to do with its physical location on or off the chip. Sorry I wasn't clear enough. BTW, isn't what you describe as "pDATA" exactly the same as "xDATA", with the only distinction being that it is accessible via the DPTR as well as R0/R1? Yes, that is entirely true - in the same way that DATA is just the bottom half of IDATA. Which devices have that construct on-chip? Is that memory like the 1 kB of xRAM on the Maxim/Dallas DS89C4x0's? I don't know - I was trying to be generic and wasn't getting into chip-specifics. With off-chip XDATA, the high byte of the address is provided by P2; with on-chip XDATA, it is chip-specific - some provide an SFR, some don't support it, etc... |
