Several functions on the Merlin board are controlled via GPIO ports that are provided by a PCA9557 circuit.
PCA9557 I2C Bus
This chip is controlled via I2C1 of the Raspberry Pi CM4 on address 0x18.
CM4_GPIO2, ALT0 → SDA
CM4_GPIO3, ALT0 → SCL
See https://datasheets.raspberrypi.com/cm4/cm4-datasheet.pdf section 2.5.1 on page 9 for details on the mapping of I/O pins.
I/O functions
PCA9557 Port | Signal | Function | J351 pin |
|---|---|---|---|
0 | LR_LED_R | 1st IR LEDs right | 10 |
1 | IR_LED_L | 1st IR LEDs left | 11 |
2 | Fix_LED_L | Fixation LED left | 9 |
3 | Fix_LED_R | Fixation LED right | 8 |
4 | IR+Fix_LED_L | 2nd IR LED left | 7 |
5 | IR+Fix_LED_R | 2nd IR LED right | 6 |
6 | CAM_PWR_OFF | Camera power | |
7 | LASER_EN | Laser | 2 |
J351 I/O connector pin assignment
Pin | Signal |
|---|---|
1 | GND |
2 | Laser power |
3 | GND |
4 | 3.3V |
5 | 3.3V |
6 | 2nd IR LED right |
7 | 2nd IR LED left |
8 | Fixation LED right |
9 | Fixation LED left |
10 | 1st IR LED right |
11 | 1st IR LED left |
12 | GND |