Post by thread:Bank switching behavior

I'm using Parallax's assembler to target a 16C57. I noticed an interesting behavior: When I use LCALL instruction to jump to a sub-routine in another bank, subsequent jump instructions (JNZ, etc) in the main code don't work correctly. This is because the LCALL sets the bank select bits. When the RET instruction is executed, these don't get reset back to the bank of the LCALL. So any 9-bit jumps go to the bank where the subroutine was located! This is easily fixed by using LSET just before the RET to set the bank select bits back to the calling bank (which means you can only call that subroutine from one bank). Example: org 00h ; bank 0 lcall other_sub ; call subroutine in bank 1 mov w, some_variable ; do something afterwards xor w, #012h jnz :not_twelve ; this jump will not work correctly! Bank select ... ; bits are set to 01. .. :not_twelve ; this line will not be reached ... ; instead, jnz will jump to somewhere in bank 1 .. org 200h ; bank 1 other_sub ; bank select bits are 01 at this point ... .. RET ; bank select bits do not change with this ret. ------- Anyone have insight on this problem? The LSET workaround is OK, but I'm wondering if I'm missing something. -- Greg Bell | "Ever see a company's sales drop sharply due to an spam_OUTgregTakeThisOuTcqt.com | annoying ad campaign? You will." ----------------------------------------------------------------------- CommQuest Technologies, Inc. (619) 633-1618 x133