Could you kindly show your command sequence here, so that we could clarify what happened?
I am not exactly sure what happened for your case, but for your questions, please see the following comments.
For Q1, the device should be in read mode during power-on.
For Q2, you are right.
There are two methods to identify the device. One has traditionally been called Autoselect and is now referred to as Device Identification (ID). The other method is called Common Flash Interface (CFI).
When reading the device ID, the sequence should be:
1. ID (Autoselect) Entry or CFI Enter
2. Read ID
3. Reset/ASO Exit
Are you waiting tVCS time after VCC crosses VCC(min) voltage before reading device ID from S29GL256S90TFI020? Please see the below screenshot from GL-S datasheet:
I'm sorry that it took time to confirm the command sequence.
Below is the actual command sequence.
【Before entering CFI Enter】(status error (code: 97))
1)Addr 555 Data AA
2)Addr 2AA Data 55
3)Addr 555 Data 90
4-1)Addr 00 Read 0001(S29GL512T10TFI020)
4-2)Addr 00 Read 0097(S29GL256S90TFI020)
5-1)Addr 01 Read 227e(S29GL512T10TFI020)
5-2)Addr 01 Read 0088(S29GL256S90TFI020)
6-1)Addr 0E Read 2223(S29GL512T10TFI020)
6-2)Addr 0E Read 0088(S29GL256S90TFI020)
7-1)Addr 0F Read 2201(S29GL512T10TFI020)
7-2)Addr 0F Read 0088(S29GL256S90TFI020)
8)Addr 555 Data F0
【After entering CFI Enter】
1)Addr 55 Data 98
2)Addr 555 Data AA
3)Addr 2AA Data 55
4)Addr 555 Data 90
5-1)Addr 00 Read 0001(S29GL512T10TFI020)
5-2)Addr 00 Read 0001(S29GL256S90TFI020)
6-1)Addr 01 Read 227e(S29GL512T10TFI020)
6-2)Addr 01 Read 227e(S29GL256S90TFI020)
7-1)Addr 0E Read 2223(S29GL512T10TFI020)
7-2)Addr 0E Read 2222(S29GL256S90TFI020)
8-1)Addr 0F Read 2201(S29GL512T10TFI020)
8-2)Addr 0F Read 2201(S29GL256S90TFI020)
9)Addr 555 Data F0
Addr 555 Data AA (ID (Autoselect) Entry) is performed in the sequence before entering CFI Enter, but status error has occurred.
What are the possible factors?
You should be able to read device ID from both of GL-S and GL-T devices without entering CFI mode. Can you check if the tVCS time is meet in your application? Please make sure that you are waiting for at least tVCS time after VCC cross VCCmin to read device ID.
Thanks and Regards,