Custom BB General

Our Computer-on-Module line of devices are required or best utilized when set on a baseboard / carrier board. We offer a number of off the shelf baseboards that we have designed to try to meet as many goals and design purposes as possible. However, some applications may require customized baseboards in order to better meet the design requirements.

This is one of the advantages of our CoM devices; end applications do not need to worry about designing and laying out the critical sections of a CPU and its peripherals. Baseboards simply break out I/O and peripherals from the module. The dual high-density connectors between the CoM and the baseboard provide a secure connection for high vibration environments.

There are a few guidelines that should be followed when laying out a custom baseboard to ensure smooth bringup and proper operation. This is divided in to multiple sections for easier access. Note that this information is purely a guideline. There may be other details required for specific applications, or some of these may not apply to every application. Technologic Systems offers custom design services, our design expertise can be used to create a custom baseboard to meet your requirements.

The TS-8200 TS-SOCKET development platform and the TS-8551 TS-SOCKET development baseboard are our recommended baseboards to use as design reference for a custom baseboard.

General CoM Guidelines

Power

• Observe the input voltage specifications. All of our CoM devices only require a single 5 VDC voltage rail input. Ensure this rail is within operational specifications of the CoM, that each 5 V power pin on the TS-SOCKET interface has a connection to this rail, and that all ground pins are connected as well. The majority of our devices can safely tolerate 5 VDC ±0.2 VDC. Be sure to not apply any other voltage to any other rails. Other voltage rails present on the TS-SOCKET connector are sequenced and output by the CoM itself. Applying voltages to these rails can cause issues at bootup or damage to the CoM.
• Observe output power specifications. Many of our CoM devices have output rails for 3.3 VDC, some even providing 1.8 VDC as well. These can be used by the baseboard and is recommended to be used versus a separate power rail on the baseboard itself if possible. However, these voltage rails should not be relied upon for heavy power draw. The majority of our devices can support around 500 mA draw from the 3.3 V rail, if not more.
• Our CoMs are designed with a suitable amount of bypassing and noise suppression for most applications. However, in environments with noisy power or high EMI, extra protection should be added to the baseboard.

I/O

• Ensure no CoM I/O pins are driven from the baseboard before the CoM power rails are valid. This is why we suggest using the CoM 3.3 VDC rail for powering devices on the baseboard where possible. If separate rails must be used, ensure that a reset circuit is created to prevent CoM I/O from being driven until the 3.3 VDC rail from the CoM is valid.
• Ensure all external I/O on the baseboard has proper ESD protection. For example, USB data lines should have TVS diodes situated near the USB host jack. Any I/O that is subject to interaction should be considered for this purpose.
• Observe maximum ratings for I/O pins. The majority of CoM I/O is 3.3 VDC with some special exceptions. However, the drive strength and trigger voltage levels may differ depending on where the I/O is routed on the CoM. The majority of I/O are able to output >= 8 mA @ 3.3 VDC, have input hysteresis, and are able to tolerate input ranges from -0.1 VDC to 3.4 VDC.

Ethernet

• Ethernet breakout requires magnetics. We recommend using jacks (Ethernet uses 8P8C modular jacks, commonly referred to as RJ45 jacks) with built-in magnetics as this is what we use on nearly all of our designs. When placing magnetics, be sure to place them as close to the TS-SOCKET interface with as little trace length variance as possible between all of the required connections.
• Ensure the correct magnetics and ethernet jack are used for the appropriate PHY. For example, CoMs with Gigabit Ethernet support require magnetics and jacks designed for Gigabit applications, even if the connected Ethernet network will only be 100BASE-T. Likewise, CoMs that support only 100 Mbit and lower require magnetics and jacks designed for 100BASE-T applications.

SD / microSD

• Many CoM devices either mirror the microSD socket that is on-board, or break out a second interface via the TS-SOCKET connector. In the case of mirrored connections, ensure that the application prevents connecting multiple SD cards to this same bus. There will likely be no damage from doing so, however it can cause headaches when debugging.
• Ensure the SD or microSD socket is placed as close as possible to the TS-SOCKET connector and that all of the SD signal lines have as little length variance as possible between them.

USB

• Run all USB lines according to USB best practices. Most CoM devices have no other components connected to the USB data lines.
• USB connectors do not need to be placed immediately next to the TS-SOCKET connector, however the data lines do need to be matched in trace length and impedance in accordance with USB standards.
• USB Host:
  • Devices can be powered from the same 5 VDC rail as the CoM. Power can optionally be controlled via a dedicated pin from the CoM. Many of our CoM devices expect to have USB device power control set on CN1_4. This pin would be connected to an electronic switch on the baseboard that can enable and disable power to the USB device.
• USB Device/OTG:
  • On CoM devices that support USB OTG, ensure the ID line is properly connected.
  • In applications where the USB OTG interface is only used as a host or a device, the ID line may still need to be connected or left floating, depending on the USB role. Additionally, it is possible in kernel configuration to force most USB OTG peripherals to be always in a single role, thereby ignoring the ID line.
  • Some CoM devices have a separate USB OTG 5 VDC line that can power devices or be used as a detect circuit for connected devices in a host role. Be sure to take precautions to not damage any USB peripherals or the CoM module/baseboard by incorrectly handling USB power.

No Connect (NC) / Unused / Reserved / JTAG Pins

• A number of pins in the TS-SOCKET pinout are marked as No Connect (NC), Reserved, Unused, as JTAG, or other programming interfaces. In most applications these pins should remain disconnected on the baseboard. Connecting them may cause issues.

RTC

• Many CoM devices have a soldered down RTC. RTC battery power is expected to come from the baseboard itself. This allows for application flexibility. e.g. A readily replaceable coin cell, a soldered down rechargeable cell, or supercapacitor solution. Note that rechargeable solutions require the baseboard design to handle charging safely. The CoM expects a constant 3.3 V source on the V_BAT pin.
• Some CoMs may require the baseboard to implement the RTC as well as the battery; with the RTC being connected via I2C or SPI. Keep this in mind while designing a custom baseboard.

Jumpers

• Many of our baseboards implement various pin jumpers. These jumpers include (but are not limited to): controlling boot flow, controlling the boot device, and adding termination resistors to bus based networks. Confirm relevant jumpers and locations for the specific CoM device when designing the baseboard.

Transcevers

• Many interfaces supported by CoM devices may require external transceivers. These include but are not limited to: CAN, RS-232 UART, and RS-485 / RS-422. The CoM I/O in most cases provides the necessary signaling at 3.3 VDC TTL levels, the baseboard is required to add any necessary transceivers to connect these signals to the bus safely.
• Some of these interfaces support or require an enable of some kind. In many cases this is a hardware assisted process like in the case of automatic TXEN on RS-485 from our FPGAs. In some cases it is software based as kernels can support using GPIO as a regulator enable or TXEN. Be sure to consider the sources of these signals when designing a custom baseboard.

Baseboard ID and Revision

• All of our off-the-shelf baseboards implement software readable ID and revision via a shift register. While not necessary for an application, it can help the bootloader identify the baseboard model as well as a specific revision. This can be used to load different kernels or behave differently for different revisions. The ID value 42 is reserved for customer use; using other values may cause issues in the future as we develop more baseboards. If it is needed, generally any ID value greater than 42 would likely also be safe.
• See the Baseboard ID section for information this mechanism and an example of how this shift register needs to be designed in to a custom baseboard.

High-Density TS-SOCKET Connectors

• The interface between a CoM and its baseboard is through a pair of gendered, keyed, high-density, 100 pin connectors. The male side needs to be installed on the baseboards as the CoM devices have the female socket. We sell the male connector directly through our store: https://www.embeddedarm.com/products/CN-TSSOCKET-M. They are from the manufacturer FCI, and the part number is "61083-102402LF"
• Note that pin 1 of the plug connector (as indicated on the plastic of the connector) may not line up with pin 1 of the TS-SOCKET specification. Be sure to properly orient the connector on the baseboard so that the silk screened pin 1 indicator on the CoM device lines up with pin 1 of the TS-SOCKET.
• See the CoM mechanical drawing for exact sizing of the module, as well as location of the high-density connectors and the mounting holes.