Interfaces

This chapter details the interfaces of the SLCam module, dividing them into three categories: electrical, software, and mechanical interfaces. Each of these categories is described in the following sections.

Electrical

All external electrical interfaces available to the user are listed in Table 4, together with their location, connector type, and pinout.

Table 4 Electrical interfaces.

Connector	Purpose	Image	Interface	Type	Pins
J1	Control/Data and power		SPI/Power	PicoBlade	1=3V3 2=GND 3=MISO 4=MOSI 5=CLK 6=CS
J3	Programming		JTAG	PinHeader	1=DIO 2=CLK 3=3V3 4=GND
J4	Control/Data		CAN	PicoBlade	1=GND 2=CAN High 3=CAN Low
J5	Debug		UART	PicoBlade	1=GND 2=UART_RX 3=UART_TX

Attention

All pins presented in Table 4 operate at CMOS 3V3 voltage level!

Software

Todas as interfaces de software do módulo estão associadas as interfaces elétricas apresentadas na seção anterior. Nas subseções a seguir, os parâmetros de configuração e características de cada interface estão descritas.

Control/Data

The control and data interfaces allow commands to be sent and their respective responses to be received, in addition to enabling data transfer from the module to the host system, such as image transmission.

Two interfaces are available for control and data transfer: the SPI and CAN interfaces. Therefore, both interfaces provide the same functionalities and enable redundant access to the device.

The specifications required to communicate with these interfaces are described in Table 5 and Table 6 (SPI and CAN, respectively).

Table 5 Control/Data interface specifications (SPI port).

Parameter	Value
PHY	SPI
Signal Level	CMOS 3V3
Mode	0 (CPHA=0/CPOL=0)
Baudrate	500 kbps
Data Link/Network Protocol	CSP
Address	10

Table 6 Control/Data interface specifications (CAN port).

Parameter	Value
PHY	CAN
Signal Level	CMOS 3V3
Type	Standard CAN
Baudrate	500 kbps
Data Link/Network Protocol	CSP
Address	11

Both interfaces use the CSP protocol [8] as the data link and network layer protocol. Commands and their respective responses are transmitted within the payload field of each CSP packet (transport layer), following the format descrided in the next section. In all CSP packets, the CRC flag must be enabled.

Commands

To externally control and access the SLCam module, some commands are available through the control/data interfaces of the board. A list with the commands is available in Table 7. The format of the commands’ answers can be seen in Table 8.

Table 7 List of commands.

ID	Name	Content	Interface
0	Read Parameter	Param. ID (1 byte)	SPI, CAN
1	Write Parameter	Param. ID (1 byte), Param. Value (8 bytes)	SPI, CAN
2	Capture Single Image	None	SPI, CAN
3	Start Automatic Capture	None	SPI, CAN
4	Stop Automatic Capture	None	SPI, CAN
5	Read Image	Image ID (4 bytes)	SPI, CAN
6	Remove Image	Image ID (4 bytes)	SPI, CAN

Table 8 Format of the command’s answers.

ID	Name	Content
1	TBD	TBD

Variables and Parameters

All variables and parameters available for reading and writing are listed in Table 9. Each variable/parameter has a unique ID and can be read by an external device. As shown, some variables can also be written.

Table 9 List of variables and parameters.

ID	Name	Description	Access	Type	Length [bytes]
0	Firmware version	v1.2.3=0x00010203	Read	uint16	2
1	Hardware version	v1.2.3=0x00010203	Read	uint16	2
2	System Time	Epoch in seconds	Read/Write	uint32	4
3	Reset Counter	Resets since factory reset	Read	uint32	4
4	Operation Mode	TBD	Read/Write	uint8	1
5	Number of Available Images	Images in memory	Read	uint16	2
6	Image Size	0=160x120, 1=176x144, 2=320x240, 3=352x288, 4=640x480, 5=800x600, 6=1024x768, 7=1280x1024, 8=1600x1200	Read/Write	uint8	1
7	Light Mode	0=Auto, 1=Sunny, 2=Cloudy, 3=Office, 4=Home	Read/Write	uint8	1
8	Color Saturation	0=Saturation 0, 1=Saturation 1, 2=Saturation 2	Read/Write	uint8	1
9	Brightness	0=Brightness 0, 1=Brightness 1, 2=Brightness 2	Read/Write	uint8	1
10	Contrast	0=Contrast 0, 1=Contrast 1, 2=Contrast 2	Read/Write	uint8	1
11	Special Effect	0=Antique, 1=Bluish, 2=Greenish, 3=Reddish, 4=Black and White, 5=Negative, 6=Negative Black and White, 7=Normal	Read/Write	uint8	1

Debug

The debug interface consists of a serial port where system log messages are written and configuration and operation commands can be sent, both through a command-line terminal interface. The communication specifications of this interface are described in Table 10.

Table 10 Debug interface specifications.

Parameter	Value
PHY	UART
Signal Level	CMOS 3V3
Baudrate	115200 bps
Data Bits	8
Stop Bits	1
Parity	None
Flow Control	XON/XOFF

An example of the output of this interface when the SLCam is connected to a computer and powered on can be seen in Fig. 14.

Fig. 14 Debug interface output example.

Programming

To upload the firmware to the module, the programming interface must be used. This interface provides a JTAG port, where an ST-Link programmer must be connected for code uploading.

Mechanical

The SLCam module provides two main external mechanical interfaces: the mounting structure and the optical interface of the camera lens. These interfaces are responsible for enabling the mechanical integration of the payload into the satellite structure while also providing the required optical access for image acquisition.

For structural integration, the module includes four 3.2 mm diameter through holes designed for the use of standard M3 screws. These mounting holes allow the SLCam to be securely attached to the satellite structure or to external support fixtures during integration and testing activities. The location of the mounting holes on the mechanical case is illustrated in Fig. 15.

Fig. 15 Mounting holes of the SLCam case.

The relative spacing and distances between the mounting holes are presented in Fig. 16. These dimensions are important for the mechanical integration of the payload and must be considered during the design of the satellite support structure and assembly interfaces.

Fig. 16 Distance between the mounting holes.