| ??? 08/18/05 07:05 Read: times |
#99621 - I do Responding to: ???'s previous message |
hi,
Abhishek Singh said:
movx @dptr,a ;store byte to destination movx a,@dptr ;readback byte from RAMwith this: isnt it that these instuctions reside in the internal program space. Yes, the instructions are fetched from internal memory and they do access to external memory (because DPTR contains 0x8000 and above). AT89c51 accesses ext mem only if 1. PC has a value greater than 1FFFh 2. EA is enabled(not the case here) You are right. But what you posted is about external program memory while MOVX does access to external data memory. For AT89C52, instruction MOVX always access external data memory and always activates /RD because AT89C52 has no internal extended data memory (XDATA). What I said once again: - When Little Joe access external RAM as external data memory via MOVX then hardware uses /RD pin and duration of read cycle is yet enough (88ns); - When Little Joe jumps to external RAM then the first fetch of instruction from external program memory utilizied /PSEN pin and fetch cycle may be not enough (50ns). Regards, Oleg |
| Topic | Author | Date |
| week puzzle III | 01/01/70 00:00 | |
| Not getting into details... | 01/01/70 00:00 | |
| you do | 01/01/70 00:00 | |
| see this | 01/01/70 00:00 | |
| Well. . . | 01/01/70 00:00 | |
| let me try | 01/01/70 00:00 | |
| eh? | 01/01/70 00:00 | |
| I`m confused with A15 | 01/01/70 00:00 | |
| Whooops | 01/01/70 00:00 | |
| and I thought that was "the puzzle" | 01/01/70 00:00 | |
| sorry | 01/01/70 00:00 | |
| and I thought that was "the puzzle" | 01/01/70 00:00 | |
| another trouble | 01/01/70 00:00 | |
| And what's wrong with /CS? | 01/01/70 00:00 | |
| sorry, my mistake | 01/01/70 00:00 | |
| what does not happend? | 01/01/70 00:00 | |
| And...? | 01/01/70 00:00 | |
| explain | 01/01/70 00:00 | |
| And...? | 01/01/70 00:00 | |
| Answer for puzzle | 01/01/70 00:00 | |
| I doubt? | 01/01/70 00:00 | |
| I doubt | 01/01/70 00:00 | |
| I agree here | 01/01/70 00:00 | |
| I wonder | 01/01/70 00:00 | |
| autodetect | 01/01/70 00:00 | |
| /PSEN | 01/01/70 00:00 | |
| there is also flaw in the reasoning | 01/01/70 00:00 | |
| Lost inverter | 01/01/70 00:00 | |
| errta | 01/01/70 00:00 | |
| Questions | 01/01/70 00:00 | |
| answers to questions | 01/01/70 00:00 | |
| Timings | 01/01/70 00:00 | |
| Ex[plain A bit more please | 01/01/70 00:00 | |
| intel app note says | 01/01/70 00:00 | |
| I do | 01/01/70 00:00 | |
| re:EA | 01/01/70 00:00 | |
| yes no doubt about it | 01/01/70 00:00 | |
| reset device | 01/01/70 00:00 | |
| three legged | 01/01/70 00:00 | |
The solution | 01/01/70 00:00 |