The underlying goal of the Glue subsystem is to satisfy the interconnection needs of the microcontroller, and to provide any forseen resources to the application specific area for future users.
System Block Diagram - Glue
ARM7 microcontroller (CPU)
- This is the ARM7 microcontroller that is the primary processor on the node. The microcontroller contains 10 bit analog to digital converters, a digital to analog converter, pulse width modulators, general purpose I/O, external interrupts, SPI interfaces, I^2 C interfaces, 2 UARTs, counters, timers, PLLs, and a USB interface. The ARM7 core runs at 60 MIPS, has 40 K Bytes of RAM, and 512 K Bytes of flash memory. There is a JTAG (Joint Test Action Group) debug port. The flash memory can be programmed through one of the UARTS.
Power decoupling
- This block provides transient decoupling between switching power supply and the logic power. The block also provides a single point ground connection between the analog ground bus and the SPS ground.
USB filtering block
- This block provides EMI and RF suppression from noize that might be picked up from the external USB bus. There is also 10 kV of surge suppression, current limiting, power decoupling, and a single point connection between IO ground and the SPS ground. Finally this block provides the 1.5 k ohm pullup to indicate this endpoint is to use USB full speed.
Power-on reset
- This block provides the reset signal required by the microcontroller. The reset is released after the SPS has come up to the proper operating voltage, and after the time required by the microcontroller to assure it is running properly.
Oscillator and divider
- This block provides the 12.0 MHz for the microcontroller system clock. Part of this block is contained within the microcontroller. This block also divides down the 12.0 MHZ by 8 to create a 1.5 MHz clock to syncronize the SPS. This SPS syncronization assures that switching noize created by the SPS remains constant and at a known frequency allowing it to be more easily filtered out should it cause problems with any of the circuits later down the road.
RTC crystal oscillator
- This block provides the 32.768 kHz clock signal used by the microcontrollers real-time clock. This block also contains the clock power to maintain the time of day clock when the node power is off.
Debug port
- This is an external connector providing standard JTAG (Joint Test Action Group) debug signals. The port also provides access to the UART used for programming the on-chip flash memory. There is also 3.3 volt power and digital ground provided on this port should a special debug feature need it.
Power Good and Shutdown
- These signals between the microcontroller and SPS will (1) allow the microcontroller to detect a good/bad power condition so it could do some possible corrective or evasive action, and (2) allow the microcontroller to shut down the node power in case of emergency or the need for a power-up reset. The hot-swap controller (circuit breaker block) will reset and restart the SPS after a specific period of time provided the external power is still acceptable.
Breakout of signals to application specific area
- This is where the future application specific portion of the node accesses the resources provided by this front-end module.
Status LEDs
- These are simple Red and Green LED's driven by microcontroller general purpose IO. The intent is to provide a future user defined status indicator for what ever reason.
Test points
- There are test points identified on the schematic and board intended for validation of specific functions, such as SPS Sync Clock, Power Good, SPS Shutdown. These typically would be used during initial testing, but my be of use later when the application specific functions are being tested and debugged.
Configuration trace-cuts or solder jumpers
- There are jumpers that can be reconfigured by doing a physical trace cut, and resolder. The configuration changes are for analog reference voltage source, and clock battery voltage source.