Monarco-HAT-Hardware-Reference-Manual

Monarco HAT Hardware Reference Manual 20190728-1
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2. Monarco HAT Overview
Note: Features denoted by “*” are currently being under development.
Additional documentation and resources can be found on: http://monarco.io
System Design 2.1.
Monarco HAT is based around ARM Cortex-M3 microcontroller (MCU) which provides a wide set of
embedded peripherals missing on the Raspberry Pi itself. It is PWMs for all digital outputs, versatile
counters including quadrature encoder signal decoders, digital-to-analog and analog-to-digital
converters and more. ARM MCU can also provide very deterministic IO timing in compare to
Raspberry Pi with Linux. We have chosen the EFM32 series MCU from Silicon Labs with 16 kB of RAM,
64 kB of FLASH memory and 32 MHz crystal clock.
Image 2.1: Monarco HAT system design schematics.
MCU also handles the RS-485 interface. By default, data are forwarded between RS-485 and
Raspberry's UART in both directions with correct buffering for half-duplex operation.
The primary communication channel between the MCU and the Raspberry Pi is SPI. The MCU UART
can be also used for in-system MCU firmware upgrade by built-in bootloader. For MCU reset and
bootloader activation, 2 GPIO signals from the RPi are used. Also 4 GPIO signals from the RPi are
routed to the MCU for optional use.
Monarco HAT also contains a Real Time Clock (RTC) backed by a battery (CR1225 type) and 1-Wire
bus controller. These are connected by I2C bus directly to the RPi. The MCU has also access to I2C
bus for case the Monarco HAT would be used as independent board without Raspberry Pi.
As industrial power supply standard is 24 volts, Monarco HAT has a switching power supply
integrated which accepts 10 to 30 volts input. The power supply block generates +12V, +5V and
+3.3V rails. RPi (and also an official 7" touchscreen if you have one) is powered from +5V rail which
can be switched off by the MCU to reset the RPi by Host Watchdog function implemented in the
MCU (needs to be enabled, please see SPI protocol specification). Also the 5V output for 1-Wire bus
is user switchable to reset devices on the bus or any other device connected.