| ??? 07/11/06 05:44 Read: times |
#120005 - correct Responding to: ???'s previous message |
hi,
Mike Collins said:
Would it be correct to manually get the address of a label defined in a lookup table to calculate the start in DPTR and then add whatever offset you need (in ACC) by adding ACC to DPL? i.e.
table: dw elm0,elm1,elm2,elm3 elm0: blah blah elm1: blah blah elm2: blah blah Yes, this way is correct. Just note about DW statement: depend on compiler it may use Big or Little Endian format to place 16-bit value into program memory. So you should take care about how to restore that address back into DPTR. For example, Keil places high byte of address firstly so I use next subroutine: ; here we have number of table (elmN) we look for in Accumulator (0...127) ; and DPTR is loaded with address of table of 16-bit pointers to them DPTR_FROM_CDPTR_AX2: ; calculate dimension over table of 16-bit values ADD A,ACC ; x2 due 16 bit ADD A,DPL MOV DPL,A JNC ADD_DPTR_END INC DPH ADD_DPTR_END: ;here DPTR contains pointer to the 16-bit address of table (elmN) ; load this address into DPTR MOV A,#1 MOVC A,@A+DPTR ; low byte of address PUSH ACC CLR A MOVC A,@A+DPTR ; high byte of address MOV DPH,A POP DPL RETRegards, Oleg |
| Topic | Author | Date |
| Lookup table, manual | 01/01/70 00:00 | |
| if you want a maintenance nightmare | 01/01/70 00:00 | |
| Lookup table | 01/01/70 00:00 | |
| Lookup table. | 01/01/70 00:00 | |
| correct | 01/01/70 00:00 | |
| big endian | 01/01/70 00:00 | |
| little endian (just to add some confusion:) | 01/01/70 00:00 | |
| little endian -8051 | 01/01/70 00:00 | |
Thanks Oleg | 01/01/70 00:00 |