14.5.4.1 RDY , #CMD and MODE[2:0] Lines
The RDY signal is driven by the target device so its ready/busy state can be monitored by the host. Hence, the target device raises the RDY line to level 1 (ready) when it is ready to process a new command and it keeps the line to level 0 (busy) while processing a command. The host must wait for the RDY line level to be 1 before sending any command.
Once the command processing is finished for the target device, it must wait for the host to release the #CMD line before raising the RDY line to level 1 again.
When the target device is ready to process a command, the host first drives the MODE[2:0] lines to encode the type of the next command to be processed by the target device. Then it asserts the #CMD to query the target to process the requested command. The table below lists four different types of commands:
| MODE[2:0] | Command | Command Description |
|---|---|---|
| 0 | CMDE | Read the value of DATA[7:0] lines and set it as the new value of the OP[7:0] register |
| 1 | ADDR0 | Read the value of DATA[15:0] lines and set it as the new value of ADDR[15:0] register |
| 2 | ADDR1 | Read the value of DATA[15:0] lines and set it as the new value of ADDR[31:16] register |
| 5 | DATA | Exchange data and/or start/resume the selected operation |
For details on OP[7:0] and ADDR[31:0], see the section Internal Registers.
The host must keep the levels of the MODE[2:0] and #CMD lines until a falling edge is detected on the RDY line. This falling edge of the RDY line indicates that the target device has acknowledged the new command and has started to process it. Now, the host can release the MODE[2:0] and #CMD lines.
Next, the host must release the #CMD line because the target device waits for the #CMD line to be released before raising the RDY line again.