3. How DA1453x Boots from host MCU ?

3.1. overview

The DA1453x Bluetooth low energy devices don’t feature any on-chip flash, the program code is executed from on-chip RAM. In this document we will focus on the host Configuration where the DA1453x image is stored in flash on the host RL78 MCU. At boot time the MCU then loads this code into DA1453x RAM. The Renesas MCU and BLE (DA1453x) chips are connected via a 4-wire UART and communicate with each other over Renesas’s proprietary GTL interface. The GTL interface will be detailed later on in this document.

../_images/host_config.svg — Figure 3 **Host Configuration**

3.2. boot options

The DA1453x bootloader serial protocol is documented in the UM-B-119 DA14585-DA14531 SW Platform Reference. The host MCU can initiate the download process by resetting the DA1453x via the reset pin (P0_0). More details in Section 5.1.

../_images/boot.svg — Figure 4 **Boot DA14531 from host MCU: implementation**

3.3. Setting Up the RL78/G23-128p:Fast Prototyping Board (RTK7RLG230CSN000BJ) and the DA1453x Pmod™

3.3.1. Introduction

This document is based on the US159-DA14531EVZ Pmod™ (DA14531 Pmod™) which incorporates the DA14531-00 SmartBond TINY™ Module and can ONLY be booted via 1-wire UART this is because the P0_0/P0_1 which are the Two-wire UART pins, are used to connect with the internal flash. The next section will explain how to boot using a 1-wire UART and switch to a 2-wire UART for operation. More information in DA14531 Module Datasheet.

The bootloader of the DA1453x support a 1-wire UART interface on pin P0_5.

../_images/1-wire.svg — Figure 5 **1-Wire UART configuration**

The default ROM booter of the DA1453x supports a 2-Wire UART interface on pin P0_0 and pin P0_1. In the DA1453x modules, these pins are already connected to the On board SPI flash. The DA14535 Pmod™ module overcomes pinning constraints with a pre-programmed secondary bootloader in flash. On startup, it transitions from the default ROM booter to the secondary bootloader, enabling 2-wire UART (on pins P0_5/ P0_6), hence the 1K ohm resistor is not needed.

../_images/2-wire.svg — Figure 6 **2-Wire UART configuration**

3.3.2. HW setup

Important

Some of the DA1453x PMOD variant comes with SPS firmware that utilizes the flash memory to store persistent data, including bonding databases and command configurations. This firmware disables the hardware reset functionality of the P0_0 pin, which is also used for flash access. As a result, booting from RA MCU is not possible with the default SPS firmware. To re-enable the hardware reset functionality and allow RA booting, the SPS firmware needs to be erased from the PMOD. The procedures is described in the US159-DA14531EVZ Firmware Upgrade tutorial.

Attach the US159-DA14531EVZ BLE Pmod™ to Pmod™ 1 (upper right). The DA14531 Pmod™ module and components should be facing up.
Connect the micro-USB cable from PC to the RL78/G23-128p micro-USB connector (J12).
Once completed, the LEDs should be illuminated as described below, and the connected boards should look like depicted below.
- LED3 (Top left of board, near USB debug port) Illuminating green.
- LED2 (right side) Illuminating also green.

../_images/board_connected.svg — Figure 7 **Setting Up the RL78/G23-128p:Fast Prototyping Board (RTK7RLG230CSN000BJ) and the DA14531 Pmod™**

Warning

A 1K ohm resistor should be added between UART RXD and TXD (P143 <—> P144) in order to boot the DA1453x Pmod™ from an RL78 Host microcontroller.
If you are using the DA14535 with 2 UART boot, the 1K ohm resistor is not needed.