A small percentage of WL1801MOD modules do not respond to the low frequency INIT phase of SDIO.
If I add a 100K pullup to WLAN_IRQ, I see a working module pull that signal low 170ms after VBAT comes up.
On a failing module, WLAN_IRQ does not pull this signal low, nor does it respond to SD INIT.
Where can I find docs on RS232_DEBUG usage?