Board Design - Milli Pins to Expose
Debug and Configuration Pin Header
Exposure of the "configuration UART" pins through a header is strongly recommended. This header is required for each of the following:
- Fast hardwired configuration (aka personalization) during board, unit and end device manufacturing.
- Fast hardwired firmware update during manufacturing, in the warehouse, or even in the field.
- Firmware image management for conducting various hardware tests or for running a Milli self test during manufacturing, certification testing, field testing, troubleshooting, or as part of the RMA process.
A 4-pin header is an integral part of any product PCBA that utilizes the Milli. The header should include the following pins (refer to the Milli Datasheet for additional information):
Pin 1: 3.3 V – any 3.3V power source although not necessary or used if a “bus powered” (e.g. USB connector) cable like the TTL-232R-RPi is used
Pin 2: RXD – Milli Pin 14 (referenced as GPIO26)
Pin 3: TXD – Milli Pin 18 (referenced as GPIO27)
Pin 4: GND
- Itron stronglhy advises a 4-pin 0.1” spacing, single-row, through hole header.
- For header and pin design refer to the drawing Samtec # TSW-104-07-G-S.
- Only pins 2-4 (i.e. no 3.3 V connection) if powered via the serial console.
- Connection can use the FTDI cable TTL-232R-RPi “USB to TTL RS232 Cable for Raspberry Pi Platform” (see datasheet) which can be purchased here.
- The Milli Dev Kit (aka Milli Shield) exposes this type of header as shown on the Dev Kit Schematics.
- There are strict power sequencing steps to be utilized, in order to prevent damaging the Milli module:
- The Milli SoC has a strict requirement that any digital I/O pins must not exceed the SoC Vcc by more than 0.3V (nominal Vcc on mNIC is 3.3V). The SoC can be permanently damaged if this sequence isn’t properly followed.
- Thus, the normal (or externally supplied from lab supplies or batteries) Vcc MUST be applied, and stabilized, at the Milli, BEFORE attaching the serial console port:
- Apply power to Milli.
- Then attach the serial console port to whatever external device is being utilized
Milli Reset Pin
The integrated device should provide a means of setting Milli reset pin which is pin 53 (RSET_N). Resetting the Milli is needed for operations such as firmware updates and configuration changes. The reset pin is activated when low, or shorting to ground. Activating this pin will restart the Milli module. This can be done through an integrated circuit, pushbutton, switch or any means to initiate a low pulse to the pin.