4.4. Plug and Play Isolation Sequence
On power up, all Plug and Play cards detect RESET_DRV, set their CSN to 0, and enter the Wait for Key state. There is a required 2 msec delay from either a RESET_DRV or ResetCmd to any Plug and Play port access to allow a card to load initial configuration information from a non-volatile device.
Cards in the Wait for Key state do not respond to any access to their auto-configuration ports until the initiation key is detected. Cards ignore all ISA accesses to their Plug and Play interface.
When the cards have received the initiation key, they enter the Sleep state. In this state, the cards listen for a Wake[CSN] command with the write data set to 0x00. This Wake[CSN] command will send all cards to the Isolation state and reset the serial identifier/resource data pointer to the beginning.
The first time the cards enter the Isolation state it is necessary to set the READ_DATA port address using the Set RD_DATA port command.
Next, 72 pairs of reads are performed to the Serial Isolation register to isolate a card as described previously. If the checksum read from the card is valid, then this means one card has been isolated. The isolated card remains in the Isolation state while all other cards have failed the isolation protocol and have returned to the Sleep state. The CSN on this card is set to a unique number. Writing this value causes this card to transition to the Config state. Sending a Wake[0] command causes this card to transition back to Sleep state and all cards with a CSN value of zero to transition to the Isolation state. This entire process is repeated until no Plug and Play cards are detected.
If a conflict is detected on the READ_DATA port, a Wake[0] command is issued to cause all the cards that are in Isolation state to reset their serial identifier/data pointer to the beginning while remaining in the Isolation state. Further, after a read port conflict has been detected and a Wake[0] has been issued, the software must wait 1 msec before beginning the next 72 pairs of serial isolation read cycles.