| ??? 12/19/06 10:55 Read: times |
#129729 - Indexing Responding to: ???'s previous message |
if I write to dph/dpl then the dptr moves automatically so that I don't need to then do a mov dptr, #blahblahblah? dpl and dph ARE the dptr, so there's no moving involved. As an ASIDE, mov dptr,#1234h might equally be written as mov dpl,#34h mov dph,#12h No difference. when you do: add a, dpl and that operation producs a carry, the carry bit is set until you clear it or another operation clears it? To be precise: add is one of the instructions from the instruction set which uses the carry flag to signify a (partial) result. After add the carry flag will show if a carry occurred during the add or not. The subtle difference being that add will ALWAYS touch the carry flag: it will not only set it if there was: it will also CLEAR IT IF THERE WASN'T. So if the carry bit was 1 before the add, and executing the add didn't produce a carry, after the add the carry flag will be 0. It is not like the add will leave carry flag unchanged if there wasn't a carry, as your statement might be interpreted. After the add, the carry flag will maintain the state to which the add set it until another instruction is executed which inherently (eg. cjne, subb or clr c) or deliberately (eg. mov psw,#0: mov doesn't inherently touch the carry flag, but if you move something to psw deliberately of course it will) touches it. In the mean time you can ignore it, test it, or execute any number of intructions which don't touch the carry flag. The addc a, dph operation (just to be sure) will add the contents of dph and the current value of the carry bit to the accumulator? Yes. |
| Topic | Author | Date |
| newbie: offsetting the dptr | 01/01/70 00:00 | |
| additional info | 01/01/70 00:00 | |
| do you have external data memory at all? | 01/01/70 00:00 | |
| Exteranal or Internal RAM | 01/01/70 00:00 | |
| In response to Jan and Neil | 01/01/70 00:00 | |
| MOVX @DPTR,A | 01/01/70 00:00 | |
| In response to Jon | 01/01/70 00:00 | |
| Indexing | 01/01/70 00:00 | |
| In response to Hans | 01/01/70 00:00 | |
| Indexing | 01/01/70 00:00 | |
| In response to Hans | 01/01/70 00:00 | |
| the reason is | 01/01/70 00:00 | |
| In response to Russell | 01/01/70 00:00 | |
| Be careful who you listen to! | 01/01/70 00:00 | |
| movx a,@dptr | 01/01/70 00:00 | |
| In response to Neil | 01/01/70 00:00 | |
| It Adds | 01/01/70 00:00 | |
| ?????? | 01/01/70 00:00 | |
| oopps no | 01/01/70 00:00 | |
| error | 01/01/70 00:00 | |
| error | 01/01/70 00:00 | |
movx/movc | 01/01/70 00:00 |