| ??? 04/10/06 15:32 Read: times |
#113975 - unclarity with movx instruction |
Hello,
i wondered about the movx instruction in combination with the addressing mode using R0 and R1. I want to store the value of the accumulator into external RAM. I know this works with "MOVX @DPTR,A", but what is the other instruction "MOVX @R0,A" for? In the instructionset i found this declaration: >MOVX @R0,A > >If operand1 is @R0 or @R1, the Accumulator is moved >to the 8-bit External Memory address indicated by >the specified Register. This instruction uses only P0 >(port 0) to output the 8-bit address and data. >P2 (port 2) is not affected. If operand2 is @R0 >or @R1 then the byte is moved from External Memory >into the Accumulator. What does this mean? What happens with the high byte of the address? Is it set to 0? Is it set to the same value as the high byte of DPTR? Does it mean, that i only can address the first 256 byte of extenal RAM? What happens if i have several peripherals mapped to the external RAM area (e.g. RAM, LCD, Flash, ...)? Do i have to use a kind of bankswitching by setting the high byte of DPTR first? Or is the area addressed by using this operation an special area of 256 byte not really located in external RAM that only can be accessed via this algorithm? How is IRAM addressed and where is it located? regards, Markus |
| Topic | Author | Date |
| unclarity with movx instruction | 01/01/70 00:00 | |
| Speed up | 01/01/70 00:00 | |
| Mistake | 01/01/70 00:00 | |
| Clarity prevails! | 01/01/70 00:00 | |
| Quicker? | 01/01/70 00:00 | |
| Quicker! | 01/01/70 00:00 | |
| assumption... | 01/01/70 00:00 | |
| Finally, you are right! | 01/01/70 00:00 | |
| MOVX @Ri | 01/01/70 00:00 | |
| since you did not have the time to find | 01/01/70 00:00 | |
| wrong answer | 01/01/70 00:00 | |
| Typo | 01/01/70 00:00 | |
| thanks Erik for the correction | 01/01/70 00:00 | |
| It is set to P0 | 01/01/70 00:00 | |
| wrong again | 01/01/70 00:00 | |
| Yes I am | 01/01/70 00:00 | |
| an example | 01/01/70 00:00 | |
| Internal XRAM | 01/01/70 00:00 | |
| not really | 01/01/70 00:00 | |
| Ports' SFR are set to 1 | 01/01/70 00:00 | |
not a port, a "page SFR" | 01/01/70 00:00 | |
| P2? | 01/01/70 00:00 | |
| Doh! | 01/01/70 00:00 | |
| which derivative | 01/01/70 00:00 | |
| do not allow? | 01/01/70 00:00 | |
| AT89S8252 | 01/01/70 00:00 | |
| Aaaaah, so. Thanks. | 01/01/70 00:00 | |
| Tanks | 01/01/70 00:00 |