Hello, I am about to use a P89c669 in a design with external program memory. Problem is that the manual states that EA pin either disables external program memory when held HIGH, or disables internal flash when EA is held LOW. The feedback I got from Philips is that when EA is held HIGH (???) both external and internal memory can be used in a mixed mode. So the big question is, if I want to use both program memories, how do I do it? I would appreciate any help on it.
Thanks beforehand Dimitris
"normal" operation for 89C5x is for EA LOW to turn the device into full 64K = External ROM [Romless], and when EA is HI, for On Chip FLASH memory to be used, where available. Above that limit, execution moves to external/off chip memory, but is dependant on lock bits. [you normally can disable off chip execution if you want - see the section on security bits for more details on Int.Ext code]
-jg
quote from the manual: "EA must be externally held LOW to enable the device to fetch code from external program memory locations. If EA is held HIGH, the device executes from internal program memory"
I think you'll agree that what you suggest isn't exactly cried out by this sentence, right? But then again, no datasheet is ever clear..Anyway, thanks for the advice, I'll give it a try.
-- Dimitris Stafylarakis
Have something to add? Share your thoughts — no account required.
Ask the community — no account required