Expansion Connectors
- 01 Oct 2021
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Expansion Connectors
- Updated on 01 Oct 2021
- 3 Minutes to read
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Introduction
There are three expansion connectors on AXON-PI.
- 40-pin Expansion Connector (J1)
- Audio Expansion Connector (J2)
- CLIX Expansion Slot (J3)
AXON Signal Name Convention
On AXON-IMX8M-MINI, there is an integrated FPGA. Almost all of the single-ended signals from the SOC are routed first to the FPGA. The FPGA then connects the signal to a signal named the same, but with an "F_" prefix to the baseboard connectors. Within the FPGA, when the axonfabric firmware is loaded, this configured via a Linux driver to bridge the signal to the matching "F_xxx" signal. For example, F_SPI_A_MISO is the MISO (Master In Slave Out) signal from the SPI_A interface, but routed through the FPGA.
[i.MX8M Mini SOC]-> SPI_A_MISO -> [ FPGA ] -> F_SPI_A_MISO
On AXON-E-IMX8M-PLUS, there is no FPGA loaded and the sigals are directly connected to I/O on the SOC, however we keep the "F_[SIGNAL]" convention on the baseboard schematic.
40-pin Expansion Connector Pinout (J1)
The following table shows the pinout of the 40-pin expansion connector (J1) on AXON-PI. All I/O signal levels are 3.3V referenced.
| Signal | Pin | Pin | Signal |
|---|---|---|---|
| 3.3V Output | 1 | 2 | V_SYS (5V) |
| I2C_A_SCL | 3 | 4 | V_SYS (5V) |
| I2C_A_SDA | 5 | 6 | GND |
| F_UART_A_RTS | 7 | 8 | F_UART_B_TXD |
| GND | 9 | 10 | F_UART_B_RXD |
| F_GPIO_X1_P72 | 11 | 12 | F_AUD_B_TXCLK |
| F_GPIO_X1_P74 | 13 | 14 | GND |
| F_GPIO_X1_P76 | 15 | 16 | F_CAN_A_TX* |
| 3.3V Output | 17 | 18 | F_CAN_A_RX* |
| F_SPI_A_MOSI | 19 | 20 | GND |
| F_SPI_A_MISO | 21 | 22 | F_CAN_B_TX* |
| F_SPI_A_SCLK | 23 | 24 | F_SPI_A_CS0 |
| GND | 25 | 26 | F_SPI_A_CS1 |
| I2C_B_SDA | 27 | 28 | I2C_B_SCL |
| F_GPIO_X1_P78 | 29 | 30 | GND |
| F_GPIO_X1_P80 | 31 | 32 | F_PWM_X2_P79 |
| F_PWM_X1_P79 | 32 | 33 | GND |
| F_AUD_B_TXFS | 35 | 36 | F_CAN_B_RX* |
| F_UART_A_CTS | 37 | 38 | F_AUD_B_RXD |
| GND | 39 | 40 | F_AUD_B_TXD |
Note regarding CAN_A and CAN_B signals
On AXON-IMX8M-MINI, these are connected to the FPGA fabric. By default, these can be used as GPIO expansion, or in the future, an FPGA-based CAN controller may be introduced. On AXON-E-IMX8M-PLUS, there is no FPGA fabric and these are connected to I/O on the SOC that can be pinmux to the CAN interfaces.
Audio Expansion Connector (J2)
Connector J2 is the audio expansion connector. It is used to connect one of the two audio busses (F_AUD_A or F_AUD_B) to the onboard audio codec (WM8960). It is also used to connect the audio busses to the TechNexion VOICEHAT board.
The AXON-PI comes prepopulated with jumpers that connect the signals from F_AUD_A to the audio codec. It is possible to move the jumpers to to able use F_AUD_B to drive the codec. When using the VOICEHAT, the jumpers are removed and the VOICEHAT plugs directly into both the 40-pin Expansion Connector (J1) and the Audio Expansion Connector (J2).
The figure below shows the position of the connector, and the jumper settings to connect either F_AUD_A or F_AUD_B to the codec.
Audio Expansion Connector Signal Levels are 1.8V
Because the VOICEHAT had already been designed and in production, and the signal level for its interfaces was already 1.8V, we have level shifters on AXON-PI to convert the audio interface signal levels from 3.3V to 1.8V for connection to the WM8960.
Audio Expansion Connector Pinout (J2)
All signals are 1.8V signal level
| Pin | Signal | Description |
|---|---|---|
| 1 | F_AUD_A_RXD_1V8 | Audio interface A receive data (driven by codec, input to AXON module) |
| 2 | CODEC_I2S_RXD | Codec audio interface receive data (driven by codec) |
| 3 | F_AUD_B_RXD0_1V8 | Audio interface B receive data (driven by codec, input to AXON module) |
| 4 | F_AUD_A_TXD_1V8 | Audio interface A transmit data (driven by module, input to codec) |
| 5 | CODEC_I2S_TXD | Codec audio interface transmit data (input to codec) |
| 6 | F_AUD_B_TXD0_1V8 | Audio interface B transmit data (driven by module, input to codec) |
| 7 | F_AUD_B_TXCLK_1V8 | Audio interface B transmit clock (driven by codec, input to module) |
| 8 | CODEC_I2S_TXCLK | Codec audio interface transmit clock (driven by codec, input to module) |
| 9 | F_AUD_A_TXCLK_1V8 | Audio interface A transmit clock (driven by codec, input to module) |
| 10 | F_AUD_B_TXFS_1V8 | Audio interface B transmit framesync (driven by codec, input to module) |
| 11 | CODEC_I2S_TXFS_1V8 | Codec audio interface transmit framesync (driven by codec, input to module) |
| 12 | F_AUD_A_TXFS_1V8 | Audio interface A transmit framesync (driven by codec, input to module) |
CLIX Expansion Connector (J3)
To be added.
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