At 01:14 PM 2/23/00 +1100, you wrote:

Hi John,

[Disclaimer. This info is valid for the 16C57, I am assuming to applies to the
16C05 which is a similar core to the 16C57 except that the '57 is 2K and
has four pages not two like the 1K '505.]

If you want to call from one page to another you need to set the page select
bits in the status register. You can look  this up in the data sheet to get
a good idea of what is required.

Each page is 512 words, not 256.

You can only call the first 256 words of each 512 page so all subroutines
need to be in the 00-FF address range.

Hopefully  someone will come along with a URL where you can download
ready-rolled macros that are better than mine below: (Some of mind do not
apply to the 1K '505.)

flags EQU 03 (STATUS for the non Z80 convertees  ;-)
pa0 equ 5
pa1 equ 6

;Call #from page, #to page

call0p1         macro a
                bsf flags,pa0
                call a
                bcf flags,pa0
                endm

call0p2         macro a
                bsf flags,pa1
                call a
                bcf flags,pa1
                endm

call1p0         macro a
                bcf flags,pa0
                call a
                bsf flags,pa0
                endm

call1p2         macro a
                bcf flags,pa0
                bsf flags,pa1
                call a
                bsf flags,pa0
                bcf flags,pa1
                endm

call2p0         macro a
                bcf flags,pa1
                call a
                bsf flags,pa1
                endm

call2p1         macro a
                bcf flags,pa1
                bsf flags,pa0
                call a
                bcf flags,pa0
                bsf flags,pa1
                endm

call3p0         macro a
                bcf flags,pa0
                bcf flags,pa1
                call a
                bsf flags,pa1
                bsf flags,pa0
                endm

gotop0          macro a
                bcf flags,pa0
                bcf flags,pa1
                goto a
                endm

gotop1          macro a
                bsf flags,pa0
                bcf flags,pa1
                goto a
                endm

gotop2          macro a
                bcf flags,pa0
                bsf flags,pa1
                goto a
                endm

gotop3          macro a
                bsf flags,pa0
                bsf flags,pa1
                goto a
                endm

-Jim


>Dear PICsters,
>I am trying to wrap my head around the paging system that the '505 uses. If
>I understand correctly, the memory is banked into four arrays of around 255
>bytes each. A call from the first bank to the second or third bank seem to
>wrap around the program counter or something which means the program somehow
>finds its way back to bank 0 . Does anyone have some tips or can explain
>this phenomena to me please? I would really appreciate it. Many thanks.
>
>                                Regards John
>
Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: newfound@pipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________