| ??? 07/19/05 12:51 Read: times |
#97625 - what Atmel says Responding to: ???'s previous message |
hi,
Hans Van Pelt said:
"When the EA pin is high, the processor fetches instructions from internal program Flash. If the EA pin is tied low, all program memory fetches are from external memory."
For which I see no exception being mentioned, which implies that this is ALWAYS the case if you tie /EA low. Period. It MAY mean that if you tie /EA low and set LB2, the CPU can't access either program memory and fetches only latch noise, but that's just guessing. Indeed, I have read that too. But I also read some more documents before post message. For example, here Atmel says: Question: Can we use ROM parts as ROMless parts?
Answer: You can use the ROM parts as ROMless parts
if the security level is below 3.Another source of my information is old Atmel .pdf file which is not on their site now. It is named "80C51 MCUs Frequently Asked Questions" dated 06/06/01. The question FAQ35 from here (page 11): FAQ35 Affected products: All microcontrollers Question: Why can the T89C51RD2 not work in ROMless mode? Answer : By default, the T89C51RD2 security locks are set on the maximum security level (level 3) to prevent piracy. This security level doesn’t allow the MOVC instruction in external execution, verify using parallel programmer, external execution. The Romless mode can be allowed if the lock bits are programmed either 0, 1 or 2 by a parallel programmer. As you may see, no /EA level is mentioned. If it would be as you said then Atmel might just say: "to run external program connect /EA to the ground". But the question is more complex and depends on lock bits as well. Regards, Oleg |
| Topic | Author | Date |
| Migration on AT89C51ED2 problem | 01/01/70 00:00 | |
| please | 01/01/70 00:00 | |
| more details, please | 01/01/70 00:00 | |
| More detail | 01/01/70 00:00 | |
| possible reasons | 01/01/70 00:00 | |
| LB2 and /EA | 01/01/70 00:00 | |
| acording datasheet | 01/01/70 00:00 | |
| Also according to the datasheet: | 01/01/70 00:00 | |
| what Atmel says | 01/01/70 00:00 | |
| ... and what does not say. | 01/01/70 00:00 | |
| pull the blasted !EA and come back to re | 01/01/70 00:00 | |
| That Atmel chip difference !!! | 01/01/70 00:00 | |
different manufacturer | 01/01/70 00:00 |