PIC16C57 have 4 pages program and each page will be 512 instruction word due to both CALL & GOTO instruction which just have 8 & 9-bit address access.
therefore, we have to use the Page selection for all program memory access. and remember the CALL just can access location for 0x00 ~ 0xFF of each page.

Please see as below code example for using the MACRO instruction PAGESEL with MPASM.

pagesel Label
call Label ( subroutine access with 0x200 ~ 0x2ff)
:
:
org 0x0200
Label movlw 0x00
movwf 0x20
:
:
return

you also can see the MPASM Presentation as below web linker if you can read the Chinese.
http://www.microchip.com.tw/modules/w ... ds/visit.php?cid=4&lid=32

Problem is solved by adding one instruction(GOTO RESET) @ 000H. It's seems my codes run to 000H

Also :
org 0x7FFH
GOTO RESET


Thanks.

Post up your code right here that we can solve the problem.

Sorry,you're right.
STATUS REGISTER (ADDRESS: 03h)
PA<1:0>: Program page preselect bits
00 = Page 0 (000h - 1FFh)
01 = Page 1 (200h - 3FFh)
10 = Page 2 (400h - 5FFh)
11 = Page 3 (600h - 7FFh)

ex:(If this code section at page0.)
BSF STATUS,PA0
CALL test2h
BCF STATUS,PA0

org 200h
test2h: retlw 0

Sorry, this ins no PCLATH register for PIC16C57, only PCL found.
But even if this subfunction is NOT used at all, it still will cause my code can't work. This is very confusing to me.
In this case, I don't bother to modify PCLATH.

If I use this subfunction, I do modify bit 5 & 6 of STATUS for page switch. But still code fails .

Check the datasheet. You must modify "PCLATH".

Dear All,
There is a strange problem when using PIC16C57.
If my main code is all ok located in page0, size 160 bytes.
Now if I just place one sub-function in page1 or 2, 3
like:
org 200h
test2h: retlw 0

Problem appears, code can't work whether test2h is invoked or not.
Please feel free to remark on this issue.

Thanks.

Emic.