How can I write a jump statement for an ISR at 00h through 44h?

[rednewguy]

i read in a book that address from 4000h to FFFFh only are programmer accessible, while others are used by the processor internally. then how can i write a jump statement for an ISR at 00h through 44h?

thanks

 

[IanP]

Re: alp-8085

I don't think this statement is correct ..

address from 4000h to FFFFh only are programmer accessible

The 8085 can access 2!16 (= 65,536) individual 8-bit memory locations, or in other words, its address space is 64k bytes ..

Regards,
IanP

 

[rednewguy]

Re: alp-8085

yes, as you said it CAN access 64k of memory. but in our college, we use a 8085 kit. it has been provided with only 32k memory. in its manual its been mentioned that programming area is 4000h to 7FFFh. they use something called loop back addressing. (0000h to BFFFh) and (C000h to FFFFh) will again point to same location as 4000 to 7FFFh.
whenever i tried to access memory less than 4000h, it automatically adds an offset of 4000h. so how to write an ISR for an interrupt at its vector address.

 

[dkk]

Re: alp-8085

You feed actual location of your ISR (may be somewhere in 4000h to 7FFFh) in the location say e.g. 00h (Corresponding to RST 0) like
00 - c3 [Code for unconditional jump, jmp 5fff]
01 - ff
02- 5f
assuming ISR is stored at 5FFFh.
Now you write your ISR at 5FFF h
Hope it answer your querry.
dKK