Hardware update – MSP430G2955 board
We got a few PCBs of the stackable version of the controller board. Today we assembled and tested two boards. This version of the controller board is populated with –
- An MSP430G2955 (16 bit micro from TI’s value line series)
- An AT24MAC602 (2 kb serial eeprom, 64 bit MAC/EUI and 128 bit serial number)
- A 32 KHz crystal
- 2 LEDs
- Two stackable (self nesting) 2×20 connectors
- Two 1×7 connectors for the radio board
- 3 pin right angled UART connector (rx, tx and gnd)
- 4 pin rigjt angled SPY-BY-WIRE connector (vcc, gnd, tdio and tck)
The MSP430G2955 is a 38/40 pin device with 4 KB RAM and 56 KB of flash.
The WiSense sensor-actuator network protocol stack is built on top of 802.15.4. This protocol requires each node to have a unique 64 bit IEEE assigned “extended” address. The AT24MAC602 provides this address. According to the device data sheet, each AT24MAC602 contains a unique IEEE-provded 64-bit pre-programmed MAC/EUI address to enable a connected device to connect to the Internet or local network.
The 32 KHz cystal provides a high accuracy clock to the micro. In addition, it allows the MSP430 to use low power mode 3 (LPM3) when it wants to sleep. In this mode, the micro’s power consumption is less than 1 micro-ampere. It is so low because (in LPM3) the CPU and all internally generated clocks are off. The micro can only be woken by an interrupt (including interrupts from on-board peripherals such as timers). The on board timer modules remain active in LPM3 if they are clocked by an external clock. This allows the micro to start a timer and then go to sleep in LPM3. When the timer expires, the corresponding interrupt from the timer module will wake up the micro out of LPM3. LPM3 is essential for implementing reduced function nodes (RFNs) which need to operate on low capacity batteries (such as non rechargeable button/coin cells).
Except for the pins used to connect to the external crystal, the remaining 36 pins of the MSP430 are available on the two 2×10 stackable connectors. These 36 pins include –
- 2 pin UART interface
- 3 pin SPI interface (SIMO, SOMI, SCLK)
- 2 pin I2c bus (implemented in software)
- 2 pin SPY-BY-WIRE interface
- GPIOs / ADC channels / Comparator channels
- Analog voltage supply and ground (AVCC / AVSS)
- Digital voltage supply and ground (DVCC / DVSS)
I will explain the need for separate digital and analog supply/gnd pins in another post.
Next up – Stackable RF boards and lots of sensor boards.