# PCBs

## PCB1 - Main Board

This is the PCB that takes the EOMA68 CPU Card.  It takes USB-OTG-style
5V @ 3A power (which is reversible), contains the LVDS converter IC for
the screen, as well as USB connections to the EC board (PCB2), a USB2
Hub and a USB Audio IC (CM108AH).

## PCB2 - Embedded Controller Board

This PCB contains an STM32F072, which is permanently powered by PCB1.
The STM32F072 monitors power, controls the on/off state of the EOMA68
CPU Card, emulates a keyboard and trackpad as USB devices and much more.

## PCB3 - Power Board

This PCB manages the battery, and provides power to both PCB1 and PCB2.
It also has a power switch (which is connected directly to the STM32F072
on PCB2 as a "soft switch").  There is also a Battery Charge Monitor
(coulomb counter).

## Specification for PCB2-to-PCB3 connector

| Pin Number | Function | Description |

| 1  | GND         |             |
| 2  | SCL         | I2C Clock (PCB2 STM32F072 Master) |
| 3  | SDA         | I2C Data                          |
| 4  | BATC_PSEL   | To Battery IC, indicates power selection            |
| 5  | BATC_CD     | From Battery IC, indicates Charge Status            |
| 6  | BATC_ALARM  | From Battery IC, indicates Interrupt |
| 7  | PWRON       | Connected to PCB3 external switch (for reset, power) |
| 8  | CHRG_IQRN   | From Battery Coulomb IC, indicates Interrupt |
| 9  | VREF_3V3    | Provided by PCB2 as Digital I/O Ref for PCB3 |
| 10 | SYS-V       | Provided by PCB3 to power PCB2 (nominal 4.2v)  |

## Specification for PCB1-to-PCB3 connector

| Pin Number | Function | Description |

| 1  | USB_OTG_5V0 | USB OTG (bi-directional) Power, up to 1.5A |
| 2  | USB_OTG_5V0 | " |
| 3  | SYS_V       | System Voltage (nominally 4.2v from battery) |
| 4  | SYS_V       | " |
| 5  | GND         | |
| 6  | GND         | |

## Specification for PCB1-to-PCB2 connector

| Pin Number | Function | Description |

| 1  | GND          | |
| 2  | USB_DM       | USB- to STM32F072 |
| 3  | USB_DP       | USB+ to STM32F072 |
| 4  | GND          |  |
| 5  | EXT_BOOT0    | BOOT selection (firmware mode) to STM32F072 (PCB2) |
| 6  | EXT_NRST     | Hard RESET of STM32F072 (PCB2) |
| 7  | PWRON_EOMA68 | From STM32F072 (PCB2) to EOMA68 (PCB1) "Power On" |
| 8  | VREFTTL      | From PCB1, used for level shifting of EXT_BOOT0 |