I2C Port Expander Support

I2C port expander support

Select the expander type in the usermod settings (or at compile time, see below). Relays are attached to expander ports using virtual pin numbers starting at 100:

Expander	Ports	Virtual pins	I2C addresses
PCF8574	8 (P0-P7)	100-107	0x20-0x27 (PCF8574A: 0x38-0x3F)
AW9523	16 (P0_0-P0_7, P1_0-P1_7)	100-107 (P0_x), 108-115 (P1_x)	0x58-0x5B (AD1/AD0 straps)

After changing the expander type, save and re-open the Usermods settings page so the pin dropdowns show the matching port names. With no expander selected (None), no expander ports are offered in the pin dropdowns.

AW9523 notes

• The chip is verified via its ID register at boot; the Info page shows whether it was found.
• Only the ports assigned to relays are (re)configured (GPIO mode, output direction, interrupts masked) - other ports of the chip are left untouched, so they remain available for other purposes.
• The P0_x port is open-drain by default in hardware. The usermod configures it as push-pull by default (recommended when driving relay/optocoupler inputs directly). Untick AW9523-pushpull (or set -D AW9523_P0_PUSHPULL=false) if your board relies on open-drain outputs with external pull-ups. P1_x is always push-pull.
• The RSTN pin of the AW9523 has an internal 100k pull-down - it must be tied high (to VCC) on the board or the chip stays in reset.

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