CCS C Software and Maintenance Offers
FAQFAQ   FAQForum Help   FAQOfficial CCS Support   SearchSearch  RegisterRegister 

ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to CCS Technical Support
Ports mapped into memory

 
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion
View previous topic :: View next topic  
Author Message
ibg



Joined: 19 Nov 2003
Posts: 22

View user's profile Send private message

Ports mapped into memory
PostPosted: Fri Jan 16, 2004 4:12 am     Reply with quote
Hi once again ;)

In the PIC18F452, the ports are mapped into memory from the direction F80h(PORTA) till F84h(PORTE).

If I read data coming from a port (let's say PORTA), are those 8 bits always place into the memory address where they are mapped (in case PORTA, in F80h)?

Thanks,

Imanol
Ttelmah
Guest
Re: Ports mapped into memory
PostPosted: Fri Jan 16, 2004 4:29 am     Reply with quote
ibg wrote:
Hi once again ;)

In the PIC18F452, the ports are mapped into memory from the direction F80h(PORTA) till F84h(PORTE).

If I read data coming from a port (let's say PORTA), are those 8 bits always place into the memory address where they are mapped (in case PORTA, in F80h)?

Thanks,

Imanol

Basically yes.
There are some 'caveats'. There is a slight electrical delay involved (both from the actual propogation times in the gates, and as the result of capacitance on the pins). So (for instance), if you write data 'out' to the address, and then immediately read the address, the capacitance on the port pins, may imply that the signals have not yet 'reached' the levels so that the read doesn't return the expected data. This is why the 'output latch', is also available on these latter chips, as a seperate register. So you have the output latch, from which you can 'read', the data pattern currently being 'driven' (for the bits being used as outputs), and the actual 'port' address, where a 'read' will return the current electrical 'state' of the pins.
Normally (so long as the load is not too silly), provided you allow at least an instruction time between a 'write', and a 'read', everything is OK.

Best Wishes
Display posts from previous:   
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group