CM3-HOME schematic

The CM3-Home schematic is made by 14 sheets. This so high division is required because it is a quite complex circuit and, furthermore, to ease the comprehension and reuse of each single module.

Starting from the block diagram below, let’s proceed with a quick description of the schematic diagram.


The Raspberry PI Compute Module 3 component is split in A, B, C blocks.

  • B block is related to the very specific, non re-mappable peripherals like USB, SD card, Cam, HDMI, etc. The B block and the devices directly attached to it are shown in the main sheet (CM3-Home file, no suffix).
  • C block is depicted in the CM3-Home_PWR sheet, together with other circuit’s power supplies.
  • A block is in the CM3-Home_IO sheet, with the list of all the re-mappable GPIOs and a brief descriptions of the attachable peripherals.

The LAN9514 device is driven by the only USB port available on CM3 and creates 4 different USB ports plus a 10/100 Mbps ethernet port.
The LAN9514 component is split in three blocks as well. A and B blocks, related to power supplies and to USB ports, are depicted in the CM3-Home_USB sheet.
C block is on the CM3-Home_Ethernet sheet together with protections and the RJ45 socket.

Another, quite complex, device is the FT4232. It is driven by one of the USB ports available from the LAN9514 and creates 4 different serial ports. Those are shown in the CM3-Home_Serial sheet. Two of them are configured as RS485 ports, one to connect the YARM module and the fourth one as a generic TTL serial port exposed on the external socket.
The debug serial port is directly available from the CM3 miniuart peripheral. The CM3 full serial peripheral is used to connect the TPUART device.

The TPUART is on the CM3-Home_KNX sheet related to KNX bus.

The CM3-Home_1-2-Wire sheet contains the 1-wire and 2-wire interfaces components (AKA TWI and I2C).

The DALI bus is on the CM3-Home_DALI sheet. The RX and TX lines are bit-banging driven on two GPIOs. Exchanging the two 0Ω resistors you can choose to use the CM3 or the YARM’s CPU to write or read the DALI signals.

In the CM3-Home_REL sheet there are the relays and the driving circuits connected to two GPIO.

In the CM3-Home_ANALOG-IN sheet there is the schematic with protections for the analog inputs designed to connect anti-tamper balanced line but usable in other ways as well. The analog inputs are connected to the [YARM peripherals because the Raspberry PI CM3 has no analog inputs.

The CM3-Home_YARM and CM3-Home_WiFi sheets are related to those interfaces.

The CM3-Home_Audio sheet contains the audio circuits, compatible with the Raspberry PI3 board. In short, to obtain a decent quality audio output, we are using the two PWM peripherals available for the left and right channels, a digital buffer to decrease the output impedance and a low pass filter.

CM3-Home – hardware reference

Allocation of the CM3L GPIO lines on CM3-Home
	GPIO 0  - I2C0 - SDA Mipi Camera
	GPIO 1  - I2C0 - SCL Mipi Camera
	GPIO 2  - IO1  - Mipi Camera
	GPIO 3  - IO0  - Mipi Camera
	GPIO 4  - NC
	GPIO 5  - NC
	GPIO 6  - NC 
	GPIO 7  - SPI CE1
	GPIO 8  - SPI CE0
	GPIO 12 - NC
	GPIO 13 - NC
	GPIO 14 - TXD0 TP-uart
	GPIO 15 - RXD0 TP-uart
	GPIO 16 - 1-Wire port
	GPIO 17 - NC
	GPIO 18 - Display backlight (1=On)
	GPIO 19 - NC
	GPIO 20 - IR receiver port
	GPIO 21 - Left relay
	GPIO 22 - Right relay
	GPIO 23 - Display RST
	GPIO 24 - Display D/C
	GPIO 25 - Display IRQ
	GPIO 26 - Available GPIO on J3
	GPIO 27 - Available GPIO on J3
	GPIO 28 - Left Input dry contact (1)
	GPIO 29 - Right Input dry contact (2)
	GPIO 30 - Light bus Rx
	GPIO 31 - Light bus Tx
	GPIO 32 - TXD1 Debug port
	GPIO 33 - RXD1 Debug port

	GPIO 34 - RGB led - Blue  - (0=On)
	GPIO 35 - RGB led - Green - (0=On)
	GPIO 36 - RGB led - Red   - (0=On)
	GPIO 37 - WiFi power-on (1=ON)
	GPIO 38 - Yarm reset
	GPIO 39 - Yarm 
	GPIO 40 - PWM0 OUT - Audio left channel
	GPIO 41 - PWM1 OUT - Audio right channel
	GPIO 42 - NC
	GPIO 43 - NC
	GPIO 44 - I2C1 SDA Groove port #1
	GPIO 45 - I2C1 SCL Groove port #1
J3 (SPI) Pinout
	 1 - 3V3 out
	 2 - 3V3 out
	 3 - SPI0 CE1          - GPIO 7
	 4 - Display backlight - GPIO 18 - (1=On)
	 5 - SPI0 CE0          - GPIO 8
	 6 - Display reset     - GPIO 23
	 7 - SPI0 MOSI         - GPIO 10
	 8 - Display D/C       - GPIO 24
	 9 - SPI0 MISO         - GPIO 9
	10 - Display IRQ       - GPIO 25
	11 - Available         - GPIO 26
	12 - Available         - GPIO 27
	13 - GND               
	14 - SPI0 SCLK         - GPIO 11
	15 - GND
	16 - GND

Serial port allocation
	/dev/ttyUSB0 - Left RS485 port
	/dev/ttyUSB1 - Yarm serial link
	/dev/ttyUSB2 - Right RS485 port
	/dev/ttyUSB3 - Serial port interface
	/dev/ttyAMA0 - TP-Bus
	/dev/ttyS0   - Debug port
Power consumption






Normal state after bootOffOnNone250mA @ 12 volt
Normal state after bootOffOffNone 225mA @ 12 volt 

CM3-HOME Mechanical Dimensions (c) Acme Systems srl