Digi ConnectCore 8X Instruction Manual

ConnectCore 8X
Hardware Design Guidelines and Checklist

Revision history—90002394
Revision Date Description
A April 2020 Initial release
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ConnectCore 8X Hardware Design Guidelines 2

ConnectCore 8X Hardware Design Guidelines 3
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Contents
About this document
Overview 5
Naming and signal conventions 5
Design checklist
Power supply 6
Boot 8
MCA 9
Console debug port 9
I2C 9
Wireless and Bluetooth 9
CPU control lines 10
PCIe 11
ADCs 11
Schematics
Bring-up guidelines
Power-up 14
Power rails 14
Verify system boot 15
ConnectCore 8X Hardware Design Guidelines 4

About this document
Overview
The purpose of this document is to ease and drive the hardware design process of
ConnectCore 8X SOM-based products. Schematics milestones keep bring-up of your designs on
track for success, and layout recommendations help achieve optimal electrical behavior.
This document, together with the ConnectCore 8X System-on-Module Hardware Reference Manual,
provide information key to ensuring a functional, quality design featuring the ConnectCore 8X module.
Naming and signal conventions
This document is written assuming the reader has a good working knowledge of common electronics
terminology. You may also encounter the following specific conventions:
Convention Definition
signal_name# A hash sign at the end of a signal name denotes that it is an active low signal.
_B An alternate way to indicate a signal is active low.
x Indicates an alphanumeric value.
Register/signal
[a:b]
Brackets after a name refer to the bits or signals contained in a register, or in a
set of related signals.
ConnectCore 8X Hardware Design Guidelines 5

Design checklist
The microprocessor used on this module, like all CMOS devices, can be driven into a latch-
up condition if any I/O pin is driven outside of its associated power rail. Care must be taken
to:
nNever drive an I/O pin beyond its positive rail or below ground.
nNever drive an I/O pin from an external power source during the power-on or reset
sequences.
nNever hot-swap the module or interrupt its ground connection to external circuitry.
Latch-up is a condition that can cause excessive current draw and result in excessive
heating of the microprocessor or its power supplies. This excessive heating can
permanently damage the microprocessor and/or its supporting components.
Power supply
☑ Item Description
1. Minimum
decoupling
capacitors
on
VSYS/VSYS2
1 x 100 uF + 1 x 10 uF + 1 x 1 uF
ConnectCore 8X Hardware Design Guidelines 6

Design checklist Power supply
ConnectCore 8X Hardware Design Guidelines 7
☑ Item Description
2. Powering
the MCA
This power line is the input power supply of the on-module MCA. It must be
powered from a dedicated 3.3 V regulator connected to the main input power
supply of the board, since it is an always-on power supply. Connect a Schottky
diode (low forward voltage drop) between the output of the regulator and the
VCC_MCA pin. MCA_VIN_DET must be tied to the output of this 3.3 V regulator1.
To allow coin-cell (low-power mode) applications, the coin-cell/supercap must be
connected to VCC_MCA again through a Schottky diode. See Coin-cell/supercap
connected to VCC_MCA through Schottky diode.
Ensure there is no series resistance between the coin-cell/supercap and the
VCC_LICELL net in the circuit linked above. It introduces a voltage drop in the
transitory from normal operation to RTC mode operation which could cause
undesirable RTC behavior.
1Digi has validated that using a comparator instead of a direct connection
drastically improves the transitory time that the system takes to go from normal
operation to RTC mode. See Comparator used for connecting MCA_VIN_DET line
used on the ConnectCore 8M Nano DVK.
3. Output
power rails
The following power rails are outputs from the ConnectCore 8X SOM:
n3V3
n1V8
nLDO3
nLDO4
nVCC_SCU_1V8
These power rails (except VCC_SCU_1V8, which must only power the boot mode
and JTAG circuitry) are intended to power external circuitry on the carrier board.
Do not connect any external power supply to these lines.
4. Input
power rails
The following power rails are inputs to the ConnectCore 8X SOM:
nLDO3IN
nLDO4IN
nVDD_USDHC1
nVDD_MIPI_DSI_DIG
nVDD_ENET0
nVDD_ESAI_SPDIF
nVDD_SPI_SAI
nVDD_QSPI0B
nVDD_CSI
Digi recommends using the module output power rails to power these power
domains of the SOM.

Design checklist Boot
ConnectCore 8X Hardware Design Guidelines 8
☑ Item Description
5.
Unconnected
power rails
By default, leave the following power rails unconnected:
nVCC_SNVS_LDO_1V8
nVDD_PCIE_DIG
nVDD_EMMC0
nNVCC_MIPI_CSI_DSI
Although these signals are not used externally, it may be helpful to leave them
accessible for debugging (test points).
Boot
☑ Item Description
1. BOOT_MODE
[1:0]
These lines select the boot mode of the SOM:
BOOT_MODE1 BOOT_MODE0 Description
0 0 Boot from fuses
0 1 Serial downloader
1 0 Boot from board settings
1 1 Reserved
Digi recommends you configure the boot mode lines to boot by default from
the internal eMMC of the module. This means:
nBOOT_MODE0 pulled-down through 100 K resistor
nBOOT_MODE1 pulled-high through 4.7 K resistor
See the ConnectCore 8X System-on-Module Hardware Reference Manual for
detailed information about the boot modes available on the SOM.
Note BOOT_MODE0 is internally pulled-low. In the castellated version, only
BOOT_MODE1 is available externally.
2.
Recover/Debug
mode (USB)
To allow the system to boot from USB as a recovery/debug method, Digi
recommends you add switches to quickly switch between the different boot
modes. See Boot mode switches for selecting the boot source of the module.

Design checklist MCA
ConnectCore 8X Hardware Design Guidelines 9
MCA
☑ Item Description
1.MCA_
RESET
Input reset line of the system. Connect a 100 K pull-up to VCC_MCA.
2. SWD_
CLK/PWR_IO
Input power on/off - suspend line of the system. Connect a 51 K pull-up to VCC_
MCA.
3. Isolate
VCC_MCA
power
domains
As much as possible, try not to mix the VCC_MCA power domain with the rest of
the power domains of the system.
4. MCA
recovery
Digi recommends you enable access to the SWD port of the MCA in the carrier
board. This will allow you to recover the MCA in case its firmware gets corrupted
and the micro-controller can no longer boot.
Console debug port
☑ Item Description
1.UART2 The default U-Boot loaded in the modules from manufacturing configures the UART2
as the console debug port. This console port can be changed to any other UART in the
system, but Digi recommends you use this UART2 as the console port so no
additional effort (such as compiling a new U-Boot, loading it through USB, etc.) are
required.
I2C
☑ Item Description
1.I2C pull-
ups
Add external pull-ups to the clock and data lines of the I2C buses. You will typically
use 4.7K resistors.
Wireless and Bluetooth
☑ Item Description
1.Wireless
SDIO
Wireless SDIO is not used by the default wireless MAC populated on the
ConnectCore 8X SOM. Leave these pads unconnected: D5, D6, D7, D8, D9, D10,
D11, D12, D13, D14 and G18.

Design checklist CPU control lines
ConnectCore 8X Hardware Design Guidelines 10
☑ Item Description
2. Bluetooth
UART
The UART1 port of the CPU is used for Bluetooth connectivity internally in the
SOM. The following pads must be left unconnected to preserve this Bluetooth
functionality:
nE13 (BT_UART1_TX)
nE12 (BT_UART1_RX)
nF12 (BT_UART1_CTS#)
nF11 (BT_UART1_RTS#)
This applies only to Wireless variants of the SOM. In non-wireless variants, the
UART1 bus is available.
3. Not
supported
functionality
Functionality associated with the following pads is not currently supported:
nB16: WLAN_RF_KILL#
nB17: BT_RF_KILL#
nF24: WLAN_LED
nF26: BT_LED
CPU control lines
☑ Item Description
1.POR_
B
POR_B is the reset line of the CPU. It is managed internally. It can be used as an
output for managing (resetting) external circuitry of the carrier board, but it must
never be driven as an input.
Even though this signal is not used externally, it may be useful to have it accessible
for debugging (test point).
2. IMX8_
ON_OFF
By default, let this pad unconnected.
3. PWR_
ON
Similar as the POR_B signal, this line is driven internally in the SOM. It is the PMIC
ON/OFF signal. It can be used externally for managing external circuitry but must
never be driven as an input.
Although this signal is not used externally, it may be helpful to leave it accessible for
debugging (test points).
4. SCU_
PMIC_
STANDBY
SCU_PMIC_STANDBY is the standby signal of the PMIC, and it is also controlled
internally in the SOM. It can be used externally for managing external circuitry, but
must never be driven as an input.